A Magnetar Just Woke Up After Three Years of Silence

When stars reach the end of their main sequence, they undergo a gravitational collapse, ejecting their outermost layers in a supernova explosion. What remains afterward is a dense, spinning core primarily made up of neutrons (aka. a neutron star), of which only 3000 are known to exist in the Milky Way Galaxy. An even rarer subset of neutron stars are magnetars, only two dozen of which are known in our galaxy.

These stars are especially mysterious, having extremely powerful magnetic fields that are almost powerful enough to rip them apart. And thanks to a new study by a team of international astronomers, it seems the mystery of these stars has only deepened further. Using data from a series of radio and x-ray observatories, the team observed a magnetar last year that had been dormant for about three years, and is now behaving somewhat differently.

The study, titled “Revival of the Magnetar PSR J1622–4950: Observations with MeerKAT, Parkes, XMM-Newton, Swift, Chandra, and NuSTAR“, recently appeared in The Astrophysical Journal. The team was led by Dr Fernando Camilo – the Chief Scientist at the South African Radio Astronomy Observatory (SARAO) – and included over 200 members from multiple universities and research institutions from around the world.

Magnetars are so-named because their magnetic fields are up to 1000 times stronger than those of ordinary pulsating neutron stars (aka. pulsars). The energy associated with these these fields is so powerful that it almost breaks the star apart, causing them to be unstable and display great variability in terms of their physical properties and electromagnetic emissions.

Whereas all magnetars are known to emit X-rays, only four have been known to emit radio waves. One of these is PSR J1622-4950 – a magnetar located about 30,000 light years from Earth. As of early 2015, this magnetar had been in a dormant state. But as the team indicated in their study, astronomers using the CSIRO Parkes Radio Telescope in Australia noted that it was becoming active again on April 26th, 2017.

At the time, the magnetar was emitting bright radio pulses every four seconds. A few days later, Parkes was shut down as part of a month-long planned maintenance routine. At about the same time, South Africa’s MeerKAT radio telescope began monitoring the star, despite the fact that it was still under construction and only 16 of its 64 radio dishes were available. Dr Fernando Camilo describes the discovery in a recent SKA South Africa press release:

“[T]he MeerKAT observations proved critical to make sense of the few X-ray photons we captured with NASA’s orbiting telescopes – for the first time X-ray pulses have been detected from this star, every 4 seconds. Put together, the observations reported today help us to develop a better picture of the behaviour of matter in unbelievably extreme physical conditions, completely unlike any that can be experienced on Earth”.

Artist’s rendering of an outburst on an ultra-magnetic neutron star, also called a magnetar. Credit: NASA/Goddard Space Flight Center

After the initial observations were made by the Parkes and MeerKAT observatories, follow-up observations were conducted using the XMM-Newton x-ray space observatory, Swift Gamma-Ray Burst Mission, the Chandra X-ray Observatory, and the Nuclear Spectroscopic Telescope Array (NuSTAR). With these combined observations, the team noted some very interesting things about this magnetar.

For one, they determined that PSR J1622-4950’s radio flux density, while variable, was approximately 100 times greater than it was during its dormant state. In addition, the x-ray flux was at least 800 times larger one month after reactivation, but began decaying exponentially over the course of a 92 to 130 day period. However, the radio observations noted something in the magnetar’s behavior that was quite unexpected.

While the overall geometry that was inferred from PSR J1622-4950’s radio emissions was consistent with what had been determined several years prior, their observations indicated that the radio emissions were now coming from a different location in the magnetosphere. This above all indicates how radio emissions from magnetars could differ from ordinary pulsars.

This discovery has also validated the MeerKAT Observatory as a world-class research instrument. This observatory is part of the Square Kilometer Array (SKA), the multi-radio telescope project that is building the world’s largest radio telescope in Australia, New Zealand, and South Africa. For its part, MeerKAT uses 64 radio antennas to gather radio images of the Universe to help astronomers understand how galaxies have evolved over time.

Aerial image of the South African MeerKAT radio telescope in the Karoo, South Africa. Credit: SKA

Given the sheer volume of data collected by these telescopes, MeerKAT relies on both cutting edge-technology and a highly-qualified team of operators. As Abbott indicated, “we have a team of the brightest engineers and scientists in South Africa and the world working on the project, because the problems that we need to solve are extremely challenging, and attract the best”.

Prof Phil Diamond, the Director-General of the SKA Organization leading the development of the Square Kilometer Array, was also impressed by the contribution of the MeerKAT team. As he stated in an SKA press release:

“Well done to my colleagues in South Africa for this outstanding achievement. Building such telescopes is extremely difficult, and this publication shows that MeerKAT is becoming ready for business. As one of the SKA precursor telescopes, this bodes well for the SKA. MeerKAT will eventually be integrated into Phase 1 of SKA-mid telescope bringing the total dishes at our disposal to 197, creating the most powerful radio telescope on the planet”.

When the SKA goes online, it will be one of the most powerful ground-based telescopes in the world and roughly 50 times more sensitive than any other radio instrument. Along with other next-generation ground-based and space-telescopes, the things it will reveal about our Universe and how it evolved over time are expected to be truly groundbreaking.

Further Reading: SKA Africa, SKA, The Astrophysical Journal

Astronomers Find The Most Distant Supernova Ever: 10.5 Billion Light-Years Away

Astronomers have discovered the most distant supernova yet, at a distance of 10.5 billion light years from Earth. The supernova, named DES16C2nm, is a cataclysmic explosion that signaled the end of a massive star some 10.5 billion years ago. Only now is the light reaching us. The team of astronomers behind the discovery have published their results in a new paper available at arXiv.

“…sometimes you just have to go out and look up to find something amazing.” – Dr. Bob Nichol, University of Portsmouth.

The supernova was discovered by astronomers involved with the Dark Energy Survey (DES), a collaboration of astronomers in different countries. The DES’s job is to map several hundred million galaxies, to help us find out more about dark energy. Dark Energy is the mysterious force that we think is causing the accelerated expansion of the Universe.

DES16C2nm was first detected in August 2016. Its distance and extreme brightness were confirmed in October that year with three of our most powerful telescopes – the Very Large Telescope and the Magellan Telescope in Chile, and the Keck Observatory, in Hawaii.

This image from 2015 shows the same area of sky before DES16C2nm exploded. Image: Mat Smith and DES collaboration.

DES16C2nm is what’s known as a superluminous supernova (SLSN), a type of supernova only discovered 10 years ago. SLSNs are the rarest—and the brightest—type of supernova that we know of. After the supernova exploded, it left behind a neutron star, which is the densest type of object in the universe. The extreme brightness of SLSNs, which can be 100 times brighter than other supernovae, are thought to be caused by material falling into the neutron star.

“It’s thrilling to be part of the survey that has discovered the oldest known supernova.” – Dr Mathew Smith, lead author, University of Southampton

Lead author of the study Dr Mathew Smith, of the University of Southampton, said: “It’s thrilling to be part of the survey that has discovered the oldest known supernova. DES16C2nm is extremely distant, extremely bright, and extremely rare – not the sort of thing you stumble across every day as an astronomer.”

Dr. Smith went on to say that not only is the discovery exciting just for being so distant, ancient, and rare. It’s also providing insights into the cause of SLSNs: “The ultraviolet light from SLSN informs us of the amount of metal produced in the explosion and the temperature of the explosion itself, both of which are key to understanding what causes and drives these cosmic explosions.”

“Now we know how to find these objects at even greater distances, we are actively looking for more of them as part of the Dark Energy Survey.” – Co-author Mark Sullivan, University of Southampton.

Now that the international team behind the Dark Energy Survey has found one of the SLSNs, they want to find more. Co-author Mark Sullivan, also of the University of Southampton, said: “Finding more distant events, to determine the variety and sheer number of these events, is the next step. Now we know how to find these objects at even greater distances, we are actively looking for more of them as part of the Dark Energy Survey.”

The instrument used by DES is the newly constructed Dark Energy Camera (DECam), which is mounted on the Victor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in the Chilean Andes. DECam is an extremely sensitive 570-megapixel digital camera designed and built just for the Dark Energy Survey.

The DECam in operation at its home in the Chilean Andes. The extremely sensitive, 570 megapixel camera is mounted on the Victor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory. Image: DES/CTIO

The Dark Energy Survey involves more than 400 scientists from over 40 international institutions. It began in 2013, and will wrap up its five year mission sometime in 2018. The DES is using 525 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. DES is designed to help us answer a burning question.

According to Einstein’s General Relativity Theory, gravity should be causing the expansion of the universe to slow down. And we thought it was, until 1998 when astronomers studying distant supernovae found that the opposite is true. For some reason, the expansion is speeding up. There are really only two ways of explaining this. Either the theory of General Relativity needs to be replaced, or a large portion of the universe—about 70%—consists of something exotic that we’re calling Dark Energy. And this Dark Energy exerts a force opposite to the attractive force exerted by “normal” matter, causing the expansion of the universe to accelerate.

“…sometimes you just have to go out and look up to find something amazing.” – Dr. Bob Nichol, University of Portsmouth.

To help answer this question, the DES is imaging 5,000 square degrees of the southern sky in five optical filters to obtain detailed information about each of the 300 million galaxies. A small amount of the survey time is also used to observe smaller patches of sky once a week or so, to discover and study thousands of supernovae and other astrophysical transients. And this is how DES16C2nm was discovered.

Study co-author Bob Nichol, Professor of Astrophysics and Director of the Institute of Cosmology and Gravitation at the University of Portsmouth, commented: “Such supernovae were not thought of when we started DES over a decade ago. Such discoveries show the importance of empirical science; sometimes you just have to go out and look up to find something amazing.”

Amazing New Views of Betelgeuse Courtesy of ALMA

This orange blob is the nearby star Betelgeuse, as imaged recently by the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA/ESO/NRAO

Just. Wow.

An angry monster lurks in the shoulder of the Hunter. We’re talking about the red giant star Betelgeuse, also known as Alpha Orionis in the constellation Orion. Recently, the Atacama Large Millimeter Array (ALMA) gave us an amazing view of Betelgeuse, one of the very few stars that is large enough to be resolved as anything more than a point of light.

Located 650 light years distant, Betelgeuse is destined to live fast, and die young. The star is only eight million years old – young as stars go. Consider, for instance, our own Sun, which has been shining as a Main Sequence star for more than 500 times longer at 4.6 billion years – and already, the star is destined to go supernova at anytime in the next few thousand years or so, again, in a cosmic blink of an eye.

Still lumpy… Betelgeuse imaged by Hubble in 1996. Hubble/ESA/STScI

An estimated 12 times as massive as Sol, Betelgeuse is perhaps a staggering 6 AU or half a billion miles in diameter; plop it down in the center of our solar system, and the star might extend out past the orbit of Jupiter.

As with many astronomical images, the wow factor comes from knowing just what you’re seeing. The orange blob in the image is the hot roiling chromosphere of Betelgeuse, as viewed via ALMA at sub-millimeter wavelengths. Though massive, the star only appears 50 milliarcseconds across as seen from the Earth. To give you some idea just how small a milliarcsecond is, there’s a thousand of them in an arc second, and 60 arc seconds in an arc minute. The average Full Moon is 30 arc minutes across, or 1.8 million milliarcseconds in apparent diameter. Betelgeuse has one of the largest apparent diameters of any star in our night sky, exceeded only by R Doradus at 57 milliarcseconds.

The apparent diameter of Betelgeuse was first measured by Albert Michelson using the Mount Wilson 100-inch in 1920, who obtained an initial value of 240 million miles in diameter, about half the present accepted value, not a bad first attempt.

You can see hints of an asymmetrical bubble roiling across the surface of Betelgeuse in the ALMA image. Betelgeuse rotates once every 8.4 years. What’s going on under that uneasy surface? Infrared surveys show that the star is enveloped in an enormous bow-shock, a powder-keg of a star that will one day provide the Earth with an amazing light show.

The bowshock created by Betelgeuse as it plows through the local interstellar medium. JAXA/Akari

Thankfully, Betelgeuse is well out of the supernova “kill zone” of 25 to 100 light years (depending on the study). Along with Spica at 250 light years distant in the constellation Virgo, both are prime nearby supernovae candidates that will on day give astronomers a chance to study the anatomy of a supernova explosion up close. Riding high to the south in the northern hemisphere nighttime sky in the wintertime, +0.5 magnitude Betelgeuse would most likely flare up to negative magnitudes and would easily be visible in the daytime if it popped off in the Spring or Fall. This time of year in June would be the worst, as Alpha Orionis only lies 15 degrees from the Sun!

An early springtime supernova in the future? Stellarium

Of course, this cosmic spectacle could kick off tomorrow… or thousands of years from now. Maybe, the light of Betelgeuse gone supernova is already on its way now, traversing the 650 light years of open space. Ironically, the last naked eye supernova in our galaxy – Kepler’s Star in the constellation Ophiuchus in 1604 – kicked off just before Galileo first turned his crude telescope towards the heavens in 1610.

You could say we’re due.

It’s Been Three Years Since We’ve Had a Supernova This Close

A supernova is one of the most impressive astronomical events anyone can possibly witness. Characterized by a massive explosion that takes place during the final stages of a massive star’s life (after billions of years of evolution), this sort of event is understandably quite rare. In fact, within the Milky Way Galaxy, a supernova event is likely to happen just once a century.

But within the Fireworks Galaxy (aka. the spiral galaxy NGC 6946), which is located 22 million light years from Earth and has half as many stars as our galaxy, supernovae are about ten times more frequent. On May 13th, while examining this galaxy from his home in Utah, amateur astronomer Patrick Wiggins spotted what was later confirmed to be a Type II supernova.

To break this magnificent astronomical event down, most supernova can be placed into two categories. Type I Supernovae occur when a smaller star has consumed all of its nuclear fuel, and then undergoes core collapse with the help of additional matter accreted from a nearby orbiting star. Type II Supernovae are the result of massive stars undergoing core collapse all on their own.

The confirmed supernova, “SN 2017aew”, which can be seen on the top right side of the “Fireworks Galaxy”. Click to see animation. Credit: Patrick Wiggins

In both cases, the result is a sudden and extreme increase in brightness, where the star blows off its outer layers and may become temporarily brighter than all the other stars in its galaxy. It then spends the next few months slowly fading until it becomes a white dwarf. It was while surveying the Fireworks galaxy with his own telescope that Wiggins noticed such a sudden burst in brightness, which had not been there just two nights before.

Wiggins finding was confirmed a day later (May 14th) by two experts in supernovae – Subo Dong and Krzysztof Z. Stanek, two professors from Peking University and Ohio State University, respectively. After conducting observations of their own, they determined that what Wiggins had witnessed was a Type II supernova, which has since been designated as SN 2017eaw.

In addition to being an amateur astronomer, Patrick Wiggins is also the public outreach educator for the University of Utah’s Department of Physics & Astronomy and the NASA Solar System Ambassador to Utah. This supernova, which was the third Wiggins has observed in his lifetime, is also the closest to Earth in three years, being about 22 million light years from Earth.

The last time a supernova was observed exploding this close to Earth was on January 22nd, 2014. At the time, students at the University of London Observatory spotted an exploding star (SN 2014J) in the nearby Cigar Galaxy (aka. M82), which is located around 12 million light years away. This was the closest supernova to be observed in recent decades.

Animation showing a comparison between M82 on Jan. 22nd, 2014 Nov. 22nd, 2013. Credit: E. Guido/N. Howes/M. Nicolini

As such, the observation of a supernova at a comparatively close distance to Earth just three years later is a pretty impressive feat. And it is an additional feather in the cap of an amateur astronomer whose resume is already quite impressive! Besides the three supernova he was observed, Wiggins has received many accolades over the years for his contributions to astronomy.

These include the Distinguished Public Service Medal, which is the highest civilian honor NASA can bestow. In addition, he discovered an asteroid in 2008 which the IAU – at Wiggin’s request – officially named “Univofutah”, in honor of the University of Utah. He is also a member of the Phun with Physics team, which provides free scientific lessons at the Natural History Museum of Utah.

Further Reading: University of Utah UNews

New Estimate Puts the Supernova Killzone Within 50 Light-Years of Earth

Composite Spitzer, Hubble, and Chandra image of supernova remnant Cassiopeia A. A new study shows that a supernova as far away as 50 light years could have devastating effects on life on Earth. (NASA/JPL-Caltech/STScI/CXC/SAO)

There are a lot of ways that life on Earth could come to an end: an asteroid strike, global climate catastrophe, or nuclear war are among them. But perhaps the most haunting would be death by supernova, because there’s absolutely nothing we could do about it. We’d be sitting ducks.

New research suggest that a supernova’s kill zone is bigger than we thought; about 25 light years bigger, to be exact.

Iron in the Ocean

In 2016, researchers confirmed that Earth has been hit with the effects from multiple supernovae. The presence of iron 60 in the seabed confirms it. Iron 60 is an isotope of iron produced in supernova explosions, and it was found in fossilized bacteria in sediments on the ocean floor. Those iron 60 remnants suggest that two supernovae exploded near our solar system, one between 6.5 to 8.7 million years ago, and another as recently as 2 million years ago.

Iron 60 is extremely rare here on Earth because it has a short half life of 2.6 million years. Any of the iron 60 created at the time of Earth’s formation would have decayed into something else by now. So when researchers found the iron 60 on the ocean floor, they reasoned that it must have another source, and that logical source is a supernova.

This evidence was the smoking gun for the idea that Earth has been struck by supernovae. But the questions it begs are, what effect did that supernova have on life on Earth? And how far away do we have to be from a supernova to be safe?

“…we can look for events in the history of the Earth that might be connected to them (supernova events).” – Dr. Adrian Melott, Astrophysicist, University of Kansas.

In a press release from the University of Kansas, astrophysicist Adrian Melott talked about recent research into supernovae and the effects they can have on Earth. “This research essentially proves that certain events happened in the not-too-distant past,” said Melott, a KU professor of physics and astronomy. “They make it clear approximately when they happened and how far away they were. Knowing that, we can consider what the effect may have been with definite numbers. Then we can look for events in the history of the Earth that might be connected to them.”

Earlier work suggested that a supernova kill zone is about 25-30 light years. If a supernova exploded that close to Earth, it would trigger a mass extinction. Bye-bye humanity. But new work suggests that 25 light years is an under-estimation, and that a supernova 50 light years away would be powerful enough to cause a mass extinction.

Supernovae: A Force Driving Evolution?

But extinction is just one effect a supernova could have on Earth. Supernovae can have other effects, and they might not all be negative. It’s possible that a supernovae about 2.6 million years ago even drove human evolution.

“Our local research group is working on figuring out what the effects were likely to have been,” Melott said. “We really don’t know. The events weren’t close enough to cause a big mass extinction or severe effects, but not so far away that we can ignore them either. We’re trying to decide if we should expect to have seen any effects on the ground on the Earth.”

Melott and his colleagues have written a new paper that focuses on the effects a supernova might have on Earth. In a new paper titled “A SUPERNOVA AT 50 PC: EFFECTS ON THE EARTH’S ATMOSPHERE AND BIOTA”, Melott and a team of researchers tried to shed light on Earth-supernova interactions.

The Local Bubble

There are a number of variables that come into play when trying to determine the effects of a supernova, and one of them is the idea of the Local Bubble. The Local Bubble itself is the result of one or more supernova explosion that occurred as long as 20 million years ago. The Local Bubble is a 300 light year diameter bubble of expanding gas in our arm of the Milky Way galaxy, where our Solar System currently resides. We’ve been travelling through it for the last five to ten million years. Inside this bubble, the magnetic field is weak and disordered.

Melott’s paper focused on the effects that a supernova about 2.6 million years ago would have on Earth in two instances: while both were within the Local Bubble, and while both were outside the Local Bubble.

The disrupted magnetic field inside the Local Bubble can in essence magnify the effects a supernova can have on Earth. It can increase the cosmic rays that reach Earth by a factor of a few hundred. This can increase the ionization in the Earth’s troposphere, which mean that life on Earth would be hit with more radiation.

Outside the Local Bubble, the magnetic field is more ordered, so the effect depends on the orientation of the magnetic field. The ordered magnetic field can either aim more radiation at Earth, or it could in a sense deflect it, much like our magnetosphere does now.

Focusing on the Pleistocene

Melott’s paper looks into the connection between the supernova and the global cooling that took place during the Pleistocene epoch about 2.6 million years ago. There was no mass extinction at that time, but there was an elevated extinction rate.

According to the paper, it’s possible that increased radiation from a supernova could have changed cloud formation, which would help explain a number of things that happened at the beginning of the Pleistocene. There was increased glaciation, increased species extinction, and Africa grew cooler and changed from predominantly forests to semi-arid grasslands.

Cancer and Mutation

As the paper concludes, it is difficult to know exactly what happened to Earth 2.6 million years ago when a supernova exploded in our vicinity. And it’s difficult to pinpoint an exact distance at which life on Earth would be in trouble.

But high levels of radiation from a supernova could increase the cancer rate, which could contribute to extinction. It could also increase the mutation rate, another contributor to extinction. At the highest levels modeled in this study, the radiation could even reach one kilometer deep into the ocean.

There is no real record of increased cancer in the fossil record, so this study is hampered in that sense. But overall, it’s a fascinating look at the possible interplay between cosmic events and how we and the rest of life on Earth evolved.


Stunning View of the Crab Nebula Just Got Five Times Better

Images of the Crab Nebula are always a treat because it has such intriguing and varied structure. Also, just knowing that this stellar explosion was witnessed and recorded by people on Earth more than 900 years ago (with the supernova visible to the naked eye for about two years) gives this nebula added fascination.

A new image just might be the biggest Crab Nebula treat ever, as five different observatories combined forces to create an incredibly detailed view, with stunning details of the nebula’s interior region.

Data from the five telescopes span nearly the entire breadth of the electromagnetic spectrum, from radio waves seen by the Karl G. Jansky Very Large Array (VLA) to the powerful X-ray glow as seen by the orbiting Chandra X-ray Observatory. And, in between that range of wavelengths, the Hubble Space Telescope’s crisp visible-light view, and the infrared perspective of the Spitzer Space Telescope.

Astronomers have produced a highly detailed image of the Crab Nebula, by combining data from telescopes spanning nearly the entire breadth of the electromagnetic spectrum. This image combines data from five different telescopes: the VLA (radio) in red; Spitzer Space Telescope (infrared) in yellow; Hubble Space Telescope (visible) in green; XMM-Newton (ultraviolet) in blue; and Chandra X-ray Observatory (X-ray) in purple. Credit: NASA, ESA, G. Dubner (IAFE, CONICET-University of Buenos Aires) et al.; A. Loll et al.; T. Temim et al.; F. Seward et al.; VLA/NRAO/AUI/NSF; Chandra/CXC; Spitzer/JPL-Caltech; XMM-Newton/ESA; and Hubble/STScI.

The Crab is 6,500 light-years from Earth and spans about 10 light-years in diameter. The supernova that created it was first witnessed in 1054 A. D. At its center is a super-dense neutron star that is as massive as the Sun but with only the size of a small town. This pulsar rotates every 33 milliseconds, shooting out spinning lighthouse-like beams of radio waves and light. The pulsar can be seen as the bright dot at the center of the image.

Scientists say the nebula’s intricate shape is caused by a complex interplay of the pulsar, a fast-moving wind of particles coming from the pulsar, and material originally ejected by the supernova explosion and by the star itself before the explosion.

A new x-ray image of the Crab Nebula by the Chandra X-ray Observatory. Credit: X-ray: NASA/CXC/SAO.

For this new image, the VLA, Hubble, and Chandra observations all were made at nearly the same time in November of 2012. A team of scientists led by Gloria Dubner of the Institute of Astronomy and Physics (IAFE), the National Council of Scientific Research (CONICET), and the University of Buenos Aires in Argentina then made a thorough analysis of the newly revealed details in a quest to gain new insights into the complex physics of the object. They are reporting their findings in the Astrophysical Journal (see the pre-print here).

About the central region, the team writes, “The new HST NIR [near infrared] image of the central region shows the well-known elliptical torus around the pulsar, composed of a series of concentric narrow features of variable intensity and width… The comparison of the radio and the X-ray emission distributions in the central region suggests the existence of a double-jet system from the pulsar, one detected in X-rays and the other in radio. None of them starts at the pulsar itself but in its environs.”

“Comparing these new images, made at different wavelengths, is providing us with a wealth of new detail about the Crab Nebula. Though the Crab has been studied extensively for years, we still have much to learn about it,” Dubner said.

A multi-wavelength layout of the Crab Nebula. Credit: (Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA/JPL/Caltech; Radio: NSF/NRAO/VLA; Ultraviolet: ESA/XMM-Newton).

Read the team’s paper: Morphological properties of the Crab Nebula: a detailed multiwavelength study based on new VLA, HST, Chandra and XMM-Newton images
Sources: Chandra, Hubble

Watch Stars Orbit The Milky Way’s Supermassive Black Hole

The Milky Way’s supermassive black hole, called Sagittarius A* (or Sgr A*), is arrowed in the image made of the innermost galactic center in X-ray light by NASA’s Chandra Observatory. To the left or east of Sgr A* is Sgr A East, a large cloud that may be the remnant of a supernova. Centered on Sgr A* is a spiral shaped group of gas streamers that might be falling onto the hole. Credit: NASA/CXC/MIT/Frederick K. Baganoff et al.

When your ordinary citizen learns there’s a supermassive black hole with a mass of 4 million suns sucking on its teeth in the center of the Milky Way galaxy, they might kindly ask exactly how astronomers know this. A perfectly legitimate question. You can tell them that the laws of physics guarantee their existence or that people have been thinking about black holes since 1783. That year, English clergyman John Michell proposed the idea of “dark stars” so massive and gravitationally powerful they could imprison their own light.

This time-lapse movie in infrared light shows how stars in the central light-year of the Milky Way have moved over a period of 14 years. The yellow mark at the image center represents the location of Sgr A*, site of an unseen supermassive black hole.
Credit: A. Eckart (U. Koeln) & R. Genzel (MPE-Garching), SHARP I, NTT, La Silla Obs., ESO

Michell wasn’t making wild assumptions but taking the idea of gravity to a logical conclusion. Of course, he had no way to prove his assertion. But we do. Astronomers  now routinely find bot stellar mass black holes — remnants of the collapse of gas-guzzling supergiant stars — and the supermassive variety in the cores of galaxies that result from multiple black hole mergers over grand intervals of time.

Some of the galactic variety contain hundreds of thousands to billions of solar masses, all of it so to speak “flushed down the toilet” and unavailable to fashion new planets and stars. Famed physicist Stephen Hawking has shown that black holes evaporate over time, returning their energy to the knowable universe from whence they came, though no evidence of the process has yet been found.

On September 14, 2013, astronomers caught the largest X-ray flare ever detected from Sgr A*, the supermassive black hole at the center of the Milky Way, using NASA’s Chandra X-ray Observatory.  This event was 400 times brighter than the usual X-ray output from the source and was possibly caused when Sgr A*’s strong gravity tore apart an asteroid in its neighborhood, heating the debris to X-ray-emitting temperatures before slurping down the remains.The inset shows the giant flare. Credit: NASA

So how do we really know a massive, dark object broods at the center of our sparkling Milky Way? Astronomers use radio, X-ray and infrared telescopes to peer into its starry heart and see gas clouds and stars whirling about the center at high rates of speed. Based on those speeds they can calculate the mass of what’s doing the pulling.

The Hubble Space Telescope took this photo of the  5000-light-year-long jet of radiation ejected from the active galaxy M87’s supermassive black hole, which is aboutt 1,000 times more massive than the Milky Way’s black hole. Although black holes are dark, matter whirling into their maws at high speed is heated to high temperature, creating a bright disk of material and jets of radiation. Credit: NASA/The Hubble Heritage Team (STScI/AURA)

In the case of the galaxy M87 located 53.5 million light years away in the Virgo Cluster, those speeds tell us that something with a mass of 3.6 billion suns is concentrated in a space smaller than our Solar System. Oh, and it emits no light! Nothing fits the evidence better than a black hole because nothing that massive can exist in so small a space without collapsing in upon itself to form a black hole. It’s just physics, something that Mr. Scott on Star Trek regularly reminded a panicky Captain Kirk.

So it is with the Milky Way, only our black hole amounts to a piddling 4 million-solar-mass light thief confined within a spherical volume of space some 27 million miles in diameter or just shy of Mercury’s perihelion distance from the Sun. This monster hole resides at the location of Sagittarius A* (pronounced A- star), a bright, compact radio source at galactic center about 26,000 light years away.

Video showing a 14-year-long time lapse of stars orbiting Sgr A*

The time-lapse movie, compiled over 14 years, shows the orbits of several dozen stars within the light year of space centered on Sgr A*. We can clearly see the star moving under the influence of a massive unseen body — the putative supermassive black hole. No observations of Sgr A* in visible light are possible because of multiple veils of interstellar dust that lie across our line of sight. They quench its light to the tune of 25 magnitudes.

Merging black holes (the process look oddly biological!). Credit: SXS

How do these things grow so big in the first place? There are a couple of ideas, but astronomers don’t honestly know for sure. Massive gas clouds around early in the galaxy’s history could have collapsed to form multiple supergiants that evolved into black holes which later then coalesced into one big hole. Or collisions among stars in massive, compact star clusters could have built up stellar giants that evolved into black holes. Later, the clusters sank to the center of the galaxy and merged into a single supermassive black hole.

Whichever you chose, merging of smaller holes may explain its origin.

On a clear spring morning before dawn, you can step out to face the constellation Sagittarius low in the southern sky. When you do, you’re also facing in the direction of our galaxy’s supermassive black hole. Although you cannot see it, does it not still exert a certain tug on your imagination?

Supernova Blast Wave Still Visible After 30 Years

30 years ago today, a supernova explosion was spotted in the southern hemisphere skies. The exploding star was located in the Large Magellanic Cloud — a satellite galaxy of the Milky Way – and Supernova 1987A was the brightest and nearest supernova explosion for modern astronomers to observe. This has provided an amazing opportunity to study the death of a star.

Telescopes around the world and in space have been keeping an eye on this event, and the latest images show the blast wave from the original explosion is still expanding, and it has plowed into a ring expelled by the pre-supernova star. The latest images and data reveal the blast is now moving past the ring.

Got a 3-D printer? You can print out your own version of SN1987A! Find the plans here.

Two different versions of 3-D printed models of SN1987A. Credit: Salvatore Orlando (INAF-Osservatorio Astronomico di Palermo) & NASA/CXC/SAO/A.Jubett et al.

Below is the latest image of this supernova, as seen by the Hubble Space Telescope. You can see it in the center of the image among a backdrop of stars, and the supernova is surrounded by gas clouds.

This new image of the supernova remnant SN 1987A was taken by the NASA/ESA Hubble Space Telescope in January 2017 using its Wide Field Camera 3 (WFC3). Credit: NASA, ESA, and R. Kirshner (Harvard-Smithsonian Center for Astrophysics and Gordon and Betty Moore Foundation) and P. Challis (Harvard-Smithsonian Center for Astrophysics)

Hubble launched in 1990, just three years after the supernova was detected, so Hubble has a long history of observations. In addition, the Chandra X-ray telescope – launched in 1999 – has been keeping an eye on the explosion too.

Here are a few animations and images of SN1987A over the years:

This scientific visualization, using data from a computer simulation, shows Supernova 1987A, as the luminous ring of material we see today.
Credits: NASA, ESA, and F. Summers and G. Bacon (STScI); Simulation Credit: S. Orlando (INAF-Osservatorio Astronomico di Palermo)
This montage shows the evolution of the supernova SN 1987A between 1994 and 2016, as seen by the NASA/ESA Hubble Space Telescope. Credit:
NASA, ESA, and R. Kirshner (Harvard-Smithsonian Center for Astrophysics and Gordon and Betty Moore Foundation) and P. Challis (Harvard-Smithsonian Center for Astrophysics)

Here’s a link to the original astronomer’s telegram announcing the detection.

Astronomers estimate that the ring material was was ejected about 20,000 years before the actual explosion took place. Then, the initial blast of light from the supernova illuminated the rings. They slowly faded over the first decade after the explosion, until the shock wave of the supernova slammed into the inner ring in 2001, heating the gas to searing temperatures and generating strong X-ray emission.

The observations by Hubble, Chandra and telescopes around the world has shed light on how supernovae can affect the dynamics and chemistry of their surrounding environment, and continue to shape galactic evolution.

See additional images and animations at the Chandra website, ESA’s Hubble website , and NASA.

Chance Discovery Of A Three Hour Old Supernova

Supernovae are extremely energetic and dynamic events in the universe. The brightest one we’ve ever observed was discovered in 2015 and was as bright as 570 billion Suns. Their luminosity signifies their significance in the cosmos. They produce the heavy elements that make up people and planets, and their shockwaves trigger the formation of the next generation of stars.

There are about 3 supernovae every 100 hundred years in the Milky Way galaxy. Throughout human history, only a handful of supernovae have been observed. The earliest recorded supernova was observed by Chinese astronomers in 185 AD. The most famous supernova is probably SN 1054 (historic supernovae are named for the year they were observed) which created the Crab Nebula. Now, thanks to all of our telescopes and observatories, observing supernovae is fairly routine.

The supernova that produced the Crab Nebula was detected by naked-eye observers around the world in 1054 A.D. This composite image uses data from NASA’s Great Observatories, Chandra, Hubble, and Spitzer, to show that a superdense neutron star is energizing the expanding Nebula by spewing out magnetic fields and a blizzard of extremely high-energy particles. The Chandra X-ray image is shown in light blue, the Hubble Space Telescope optical images are in green and dark blue, and the Spitzer Space Telescope’s infrared image is in red. The size of the X-ray image is smaller than the others because ultrahigh-energy X-ray emitting electrons radiate away their energy more quickly than the lower-energy electrons emitting optical and infrared light. The neutron star is the bright white dot in the center of the image.
The supernova that produced the Crab Nebula was detected by naked-eye observers around the world in 1054 A.D. This composite image uses data from NASA’s Great Observatories, Chandra, Hubble, and Spitzer.

But one thing astronomers have never observed is the very early stages of a supernova. That changed in 2013 when, by chance, the automated Intermediate Palomar Transient Factory (IPTF) caught sight of a supernova only 3 hours old.

Spotting a supernovae in its first few hours is extremely important, because we can quickly point other ‘scopes at it and gather data about the SN’s progenitor star. In this case, according to a paper published at Nature Physics, follow-up observations revealed a surprise: SN 2013fs was surrounded by circumstellar material (CSM) that it ejected in the year prior to the supernova event. The CSM was ejected at a high rate of approximately 10 -³ solar masses per year. According to the paper, this kind of instability might be common among supernovae.

SN 2013fs was a red super-giant. Astronomers didn’t think that those types of stars ejected material prior to going supernova. But follow up observations with other telescopes showed the supernova explosion moving through a cloud of material previously ejected by a star. What this means for our understanding of supernovae isn’t clear yet, but it’s probably a game changer.

Catching the 3-hour-old SN 2013fs was an extremely lucky event. The IPTF is a fully-automated wide-field survey of the sky. It’s a system of 11 CCD’s installed on a telescope at the Palomar Observatory in California. It takes 60 second exposures at frequencies from 5 days apart to 90 seconds apart. This is what allowed it to capture SN 2013fs in its early stages.

The 48 inch telescope at the Palomar Observatory. The IPTF is installed on this telescope. Image: IPTF/Palomar Observatory

Our understanding of supernovae is a mixture of theory and observed data. We know a lot about how they collapse, why they collapse, and what types of supernovae there are. But this is our first data point of a SN in its early hours.

SN 2013fs is 160 million light years away in a spiral-arm galaxy called NGC7610. It’s a type II supernova, meaning that it’s at least 8 times as massive as our Sun, but not more than 50 times as massive. Type II supernovae are mostly observed in the spiral arms of galaxies.

A supernova is the end state of some of the stars in the universe. But not all stars. Only massive stars can become supernova. Our own Sun is much too small.

Stars are like dynamic balancing acts between two forces: fusion and gravity.

As hydrogen is fused into helium in the center of a star, it causes enormous outward pressure in the form of photons. That is what lights and warms our planet. But stars are, of course, enormously massive. And all that mass is subject to gravity, which pulls the star’s mass inward. So the fusion and the gravity more or less balance each other out. This is called stellar equilibrium, which is the state our Sun is in, and will be in for several billion more years.

But stars don’t last forever, or rather, their hydrogen doesn’t. And once the hydrogen runs out, the star begins to change. In the case of a massive star, it begins to fuse heavier and heavier elements, until it fuses iron and nickel in its core. The fusion of iron and nickel is a natural fusion limit in a star, and once it reaches the iron and nickel fusion stage, fusion stops. We now have a star with an inert core of iron and nickel.

Now that fusion has stopped, stellar equilibrium is broken, and the enormous gravitational pressure of the star’s mass causes a collapse. This rapid collapse causes the core to heat again, which halts the collapse and causes a massive outwards shockwave. The shockwave hits the outer stellar material and blasts it out into space. Voila, a supernova.

The extremely high temperatures of the shockwave have one more important effect. It heats the stellar material outside the core, though very briefly, which allows the fusion of elements heavier than iron. This explains why the extremely heavy elements like uranium are much rarer than lighter elements. Only large enough stars that go supernova can forge the heaviest elements.

In a nutshell, that is a type II supernova, the same type found in 2013 when it was only 3 hours old. How the discovery of the CSM ejected by SN 2013fs will grow our understanding of supernovae is not fully understood.

Supernovae are fairly well-understood events, but their are still many questions surrounding them. Whether these new observations of the very earliest stages of a supernovae will answer some of our questions, or just create more unanswered questions, remains to be seen.

A New Prototype Telescope Proves Itself Worthy

In 2013, the Cherenkov Telescope Array (CTA) was established with the intention of building the world’s largest and most sensitive high-energy gamma ray observatory. Consisting of over 1350 scientists from 210 research institutes in 32 countries, this observatory will use 100 telescopes across the northern and southern hemispheres to explore the high-energy Universe.

Key to their efforts is a prototype dual-mirror Schwarzschild-Couder telescope, known as the Astrofisica con Specchi a Tecnologia Replicante Italiana (ASTRI). Since it was first created in 2014, this prototype has been undergoing tests at the Serra La Nave Observing Station on Mount Etna, Sicily. And as of October of 2016, it passed its most important test to date, demonstrating a constant point-spread function across its full field of view.

The ASTRI telescope is essentially a revolutionary kind of Imaging Atmospheric Cherenkov Telescope (IACT). These ground-based telescopes are used by astronomers to detect cosmic high-energy gamma rays. These rays are produced by the most energetic objects in the universe (i.e. pulsars, supernovae, regions around black holes), and are only detectable because of the Cherenkov Effect, which they undergo once they pass into our atmosphere.

A IACT telescope at the Whipple Observatory, Mount Hopkins, Arizona. Credit: magic.mpp.mpg.de
A IACT telescope at the Whipple Observatory, Mount Hopkins, Arizona. Credit: magic.mpp.mpg.de

This effect occurs when particles of light achieve speeds greater than the phase velocity of light in their particular medium. In this case, the effect is produced when light particles pass from the vacuum of space into our atmosphere, temporarily exceeding the speed of light in air and producing a glow in the blue to UV range. In the case of very-high-energy gamma rays, indirect observations of this Cherenkov radiation is the only way to detect them.

Typically, Cherenkov telescopes use a mirror to collect light and focus it on a camera. The ASTRI telescope is something quite different, in that it is based on the Schwarzschild-Couder model. As Giovanni Pareschi, an astronomer at the INAF-Brera Astronomical Observatory and the principal investigator of the ASTRI project, told Universe Today via email:

“The ASTRI telescope for the first time is based on a two mirror imaging configuration (while in general Cherenkov telescopes work with in single mirror configuration, i.e. just a big primary mirror with the camera put in the Newtonian focus and a  f-number close to 1). ASTRI is a prototype of the telescopes of the Small Size Telescope sub-array of the CTA Observatory. The sub-array is devoted to detect the gamma rays with the highest energy (up to 100 Tev).  In order to properly work, the sub-array has to be based on a large number of telescopes (70 units) with a distance from each other of a 250 m distributed and with a large field (10 deg x 10 deg) of view with a constant angular resolution of a few arc minutes across the field of view.

This idea for such a telescope was first proposed in 1905 by German astronomer Karl Schwarzschild, but remained dormant for almost a century since it was deemed too difficult and too expensive to construct. It was not until 2007 that it was considered as a viable means for creating a new type of IACT. And in 2014, the INAF-Brera Astronomical Observatory commissioned the first of its kind to be built.

Polaris, the North Star, as observed by ASTRI with different offsets from the optical axis of the telescope. Credits: Enrico Giro/Rodolfo Canestrari/Salvo Scuderi/Giorgia Sironi/INAF
Polaris, the North Star, as observed by ASTRI with different offsets from the optical axis of the telescope. Credits: Enrico Giro/Rodolfo Canestrari/Salvo Scuderi/Giorgia Sironi/INAF

“[W]e have for the first time adopted a two reflection design based on the Schwarzschild-Couder configuration never realized before (also for telescopes operating in the visible band),” added Pareschi. “This configuration allows us to optimize the angular resolution across the field of view and to use focal plane cameras of small dimensions (thanks to this property, we could use new solid-state technology based Silicon photomultiplier sensors instead of the “old” classical photomultiplier tubes used so far in Cherenkov astronomy).”

These advantages, and the advances they allow for, will make ASTRI telescope approximately ten times more sensitive than current instruments. And with this latest test – which demonstrating a constant point-spread function of a few arc minutes over a large field of view of 10 degrees – the team behind it now has proof that it will work. As Pareschi explained:

“The test demonstrated for the first time that a telescope based on the Schwarzschild-Couder configuration correctly works and that a two-mirror configuration can be adopted for making Cherenkov telescopes for gamma ray astronomy. In addition, the ASTRI prototype has been completely characterized and validated from the opto-mechanical point of view, demonstrating that we can now proceed with the construction of the Small-Sized Telescopes (SSTs) of the array based on the ASTRI design.”

With this important test complete, the INAF-Brera team hopes to spend the next few months prepping the telescope. This will include mounting the Cherenkov camera onto the prototype and testing its gamma-ray performance. Then they will start to produce the first set of ASTRI telescopes to create a mini-array, which will serve as a precursor to the planned CTA sub-array that is scheduled to be built in Chile.

Artist’s impression of a gamma-ray burst. Credit: ESO/A. Roquette
Artist’s impression of a gamma-ray burst. Credit: ESO/A. Roquette

Once the camera is tested and mounted, the ASTRI team will conduct their first observations of gamma-rays at very high energies. These observations will allow scientists to determine the direction of gamma-ray photons that are the result of celestial sources, such as neutron stars, pulsars, supernovae, and black holes, tracing them back to their respective sources.

And with the planned construction of 100 SSTs to be spread out over the northern and southern hemispheres, the CTA array will outnumber all other telescopes in the world. The wide coverage and large number of these telescopes, spread over a wide area, will improve astronomers chances of detecting very high-energy gamma rays as they pass into our atmosphere.

Further Reading: CTA