Whittling Away At SN1987A

A team of Australian astronomers has been busy utilizing some of the world’s leading radio telescopes located in both Australia and Chile to carve away at the layered remains of a relatively new supernova. Designated as SN1987A, the 28 year-old stellar cataclysm came to Southern Hemisphere observer’s attention when it sprang into action at the edge of the Large Magellanic Cloud some two and a half decades ago. Since then, it has provided researchers around the world with a ongoing source of information about one of the Universe’s “most extreme events”.

Representing the University of Western Australia node of the International Centre for Radio Astronomy Research, PhD Candidate Giovanna Zanardo led the team focusing on the supernova with the Australia Telescope Compact Array (ATCA) in New South Wales. Their observations took in the wavelengths spanning the radio to the far infrared.

“By combining observations from the two telescopes we’ve been able to distinguish radiation being emitted by the supernova’s expanding shock wave from the radiation caused by dust forming in the inner regions of the remnant,” said Giovanna Zanardo of the International Centre for Radio Astronomy Research (ICRAR) in Perth, Western Australia.

“This is important because it means we’re able to separate out the different types of emission we’re seeing and look for signs of a new object which may have formed when the star’s core collapsed. It’s like doing a forensic investigation into the death of a star.”

“Our observations with the ATCA and ALMA radio telescopes have shown signs of something never seen before, located at the centre or the remnant. It could be a pulsar wind nebula, driven by the spinning neutron star, or pulsar, which astronomers have been searching for since 1987. It’s amazing that only now, with large telescopes like ALMA and the upgraded ATCA, we can peek through the bulk of debris ejected when the star exploded and see what’s hiding underneath.”

A video compilation showing Supernova Remnant 1987A as seen by the Hubble Space Telescope in 2010, and by radio telescopes located in Australia and Chile in 2012. The piece ends with a computer generated visualization of the remnant showing the possible location of a Pulsar. Credit: Dr Toby Potter, ICRAR-UWA, Dr Rick Newton, ICRAR-UWA

But, there is more. Not long ago, researchers published another paper which appeared in the Astrophysical Journal. Here they made an effort to solve another unanswered riddle about SN1987A. Since 1992 the supernova appears to be “brighter” on one side than it does the other! Dr. Toby Potter, another researcher from ICRAR’s UWA node took on this curiosity by creating a three-dimensional simulation of the expanding supernova shockwave.

“By introducing asymmetry into the explosion and adjusting the gas properties of the surrounding environment, we were able to reproduce a number of observed features from the real supernova such as the persistent one-sidedness in the radio images”, said Dr. Toby Potter.

So what’s going on? By creating a model which spans over a length of time, researchers were able to emulate an expanding shock front along the eastern edge of the supernova remnant. This region moves away more quickly than its counterpart and generates more radio emissions. When it encounters the equatorial ring – as observed by the Hubble Space Telescope – the effect becomes even more pronounced.

A visualization showing how Supernova1987A evolves between May of 1989 and July of 2014. Credit: Dr Toby Potter, ICRAR-UWA, Dr Rick Newton, ICRAR-UWA

“Our simulation predicts that over time the faster shock will move beyond the ring first. When this happens, the lop-sidedness of radio asymmetry is expected to be reduced and may even swap sides.”

“The fact that the model matches the observations so well means that we now have a good handle on the physics of the expanding remnant and are beginning to understand the composition of the environment surrounding the supernova – which is a big piece of the puzzle solved in terms of how the remnant of SN1987A formed.”

Original Story Source: Astronomers dissect the aftermath of a Supernova – International Centre for Radio Astronomy Research News Release.

Nearby Galaxy Holds First Ultraluminous X-Ray Source that is a Pulsar

A research team led by Caltech astronomers of Pasadena California have discovered an ultraluminous X-ray (ULX) source that is pulsating. Their analysis concluded that the source in a nearby galaxy – M82 – is from a rotating neutron star, a pulsar. This is the first ULX source attributed to a pulsar.

Matteo Bachetti of the Université de Toulouse in France first identified the pulsating source and is the lead author of the paper, “An ultraluminous X-ray source powered by an accreting neutron star” in the journal Nature. Caltech astronomer Dr. Fiona Harrison, the team leader, stated “This compact little stellar remnant is a real powerhouse. We’ve never seen anything quite like it. We all thought an object with that much energy had to be a black hole.”

What is most extraordinary is that this discovery places even more strain on theories already hard pressed to explain the existence of ultraluminous X-Ray sources. The burden falls on the shoulder of the theorists.

The NuStar Space Telescope launched into Earth orbit by a Orbital Science Corp. Pegasus rocket, 2012. The Wolter telescope design images throughout a spectral range from 5 to 80 KeV. (Credit: NASA/Caltech-JPL)
The NuStar Space Telescope launched into Earth orbit by a Orbital Science Corp. Pegasus rocket, 2012. The Wolter telescope design images throughout a spectral range from 5 to 80 KeV. (Credit: NASA/Caltech-JPL)

The source of the observations is the NuSTAR space telescope, a SMEX class NASA mission. It is a Wolter telescope that uses grazing incidence optics, not glass (refraction) or mirrors (reflection) as in visible light telescopes. The incidence angle of the X-rays must be very shallow and consequently the optics are extended out on a 10 meter (33 feet) truss. NuSTAR records its observations with a time stamp such as taking a video of the sky. The video recording in high speed is not in visible everyday light but what is called hard x-rays. Only gamma rays are more energetic. X-rays emanate from the most powerful sources and events in the Universe. NuStar observes in the energy range of X-Rays from 5 to 80 KeV (electron volt)while the famous Chandra space telescope observes in the .1 to 10 KeV range. Chandra is one NASA’s great space telescope, was launched by the Space Shuttle Columbia (STS-93) in 1999. Chandra has altered our view of the Universe as dramatically as the first telescope constructed by Galileo. NuSTAR carries on the study of X-rays to higher energies and with greater acuity.

ULX sources are rare in the Universe but this is the first pulsating ULX. After analysis, they concluded that this is not a black hole but rather its little brother, a spinning neutron star as the source. More specifically, this is an accreting binary pulsar; matter from a companion star is being  gravitationally attracted by and accreting onto the pulsar.

The Crab Nebula Pulsar, M1. Both are sequences of observations that show the expansion of shock waves emanating from the Pulsar interacting with the surrounding nebula. The Crab Pulsar actually pulsates 30 times per second a result of its rotation rate and the relative offset of the magnetic pole. Charndra X-Rays (left), Hubble Visible light (right). (Credit: NASA, JPL-Caltech)
The prime example of a pulsar – the Crab Nebula Pulsar, M1. These actual observations show the expansion of shock waves emanating from the Pulsar interacting with the surrounding nebula. The Crab Pulsar actually pulsates 30 times per second, not seen here, a result of its rotation rate and the relative offset of the magnetic pole. Charndra X-Rays (left), Hubble Visible light (right). (Credit: NASA, JPL-Caltech)

Take a neutron star and spin it up to anywhere from 700 rotations per second to a mere one  rotation every 10 seconds. Now you have a neutron star called a pulsar. Spinning or not, these are the remnants of supernovae, stellar explosions that can outshine a galaxy of 300 billion stars. Just one teaspoon of neutron star material weighs 10 million tons (9,071,847,400 kg). That is the same weight as 900 Great Pyramids of Giza all condensed to one teaspoon. As incredible a material and star that a neutron star is, they were not thought to be the source of any ultraluminous X-Ray sources. This view has changed with the analysis of observations by this research team utilizing NuSTAR. The telescope name – NuSTAR – stands for Nuclear Spectroscopic Telescope Array.

There is nothing run of the mill about black holes. Dr. Stephen Hawking only conceded after 25 years, in 2004 (the Thorne-Hawking Bet)  that Black Holes exist. And still today it is not absolutely certain. Recall the Universe Today weekly – Space Hangout on September 26 – “Do Black Holes exist?” and the article by Jason Major, “There are no such things as Black Holes.

Pulsars stars are nearly as exotic as black holes, and all astronomers accept the existence of these spinning neutron stars. There are three final states of a dying star. Stars like our Sun at the end of their life become very dense White Dwarf stars, about the size of the Earth. Neutron stars are the next “degenerate” state of a dying exhausted star. All the electrons have merged with the protons in the material of the star to become neutrons. A neutron star is a degenerate form of matter effectively made up of all neutron particles. Very dense, these stars are really small, the size of cities, about 16 miles in diameter. The third type of star in its final state is the Black Hole.

The Crab Nebula was first  observed in the 1700s and is catalogued Messier object, M1. The remant explosion of a SuperNova, Chinese astronomers observed in 1054 A.D and holds the second Pular discovered (1968).
The Crab Nebula was first observed in the 1700s and is catalogued Messier object, M1. The remant explosion of a SuperNova that Chinese astronomers observed in 1054 A.D, it holds the second Pulsar discovered (1968).

A spinning neutron star creates a magnetic field, the most powerful of such fields in the Universe. They are like a dipole of a bar magnet and because of how magnetic fields confine the hot gases – plasma – of the neutron star, constant streams of material flow down and light streams out from the magnetic poles.

Recently, the Earth has had incredible northern lights, aurora. These lights are also from hot gases — a plasma — at the top of our atmosphere. Likewise, hot energetic particles from the Sun are funneled down into the magnetic poles of the Earth’s field that creates the northern lights. For spinning neutron stars – pulsars – the extreme light from the magnetic poles are like beacons. Just like our Earth, the magnetic poles and the spin axis poles do not coincide. So the intense beacon of light will rotate around and periodically point at the Earth. The video of the first illustration describes this action.

Messier object - M82, the Cigar Nebula, nicknamed for the shape seen through telescopes of the 1800s. This is the location of the newly discovered Pulsar.
Messier object – M82, the Cigar Nebula, nicknamed for the shape seen through telescopes of the 1800s. This is the location of the newly discovered Pulsar.

The light beacons from pulsars are very bright but theory, until now, has been supported by observations. No ultraluminous X-ray sources should be pulsars. The newly discovered pulsar is outputting 100 times more energy than any other. Discoveries like the one by these astronomers utilizing NuSTAR is proof that there remains more to discover and understand and new telescopes will be conceived to help resolve questions raised by NuSTAR or Chandra.

Further reading: JPL

Split-Personality Pulsar Switches From Radio To Gamma-Rays

Another snapshot of our strange universe: astronomers recently caught a pulsar — a particular kind of dense star — switch off its radio beacon while powerful gamma rays brightened fivefold.

“It’s almost as if someone flipped a switch, morphing the system from a lower-energy state to a higher-energy one,” stated lead researcher Benjamin Stappers, an astrophysicist at the University of Manchester, England.

“The change appears to reflect an erratic interaction between the pulsar and its companion, one that allows us an opportunity to explore a rare transitional phase in the life of this binary.”

The binary system includes pulsar J1023+0038 and another star that has a fifth of the mass of the sun. They’re close orbiting, spinning around each other every 4.8 hours. This means the companion’s days are numbered, because the pulsar is pulling it apart.

In NASA’s words, here is what is going on:

In J1023, the stars are close enough that a stream of gas flows from the sun-like star toward the pulsar. The pulsar’s rapid rotation and intense magnetic field are responsible for both the radio beam and its powerful pulsar wind. When the radio beam is detectable, the pulsar wind holds back the companion’s gas stream, preventing it from approaching too closely. But now and then the stream surges, pushing its way closer to the pulsar and establishing an accretion disk.

Gas in the disk becomes compressed and heated, reaching temperatures hot enough to emit X-rays. Next, material along the inner edge of the disk quickly loses orbital energy and descends toward the pulsar. When it falls to an altitude of about 50 miles (80 km), processes involved in creating the radio beam are either shut down or, more likely, obscured.

The inner edge of the disk probably fluctuates considerably at this altitude. Some of it may become accelerated outward at nearly the speed of light, forming dual particle jets firing in opposite directions — a phenomenon more typically associated with accreting black holes. Shock waves within and along the periphery of these jets are a likely source of the bright gamma-ray emission detected by Fermi.

You can read more about the research in the Astrophysical Journal or in preprint version on Arxiv.

Source: NASA

An Earth-size Diamond in the Sky: The Coolest Known White Dwarf Detected

We live in a vast, dark Universe, which makes the smallest and coolest objects extremely difficult to detect, save for a stroke of luck. Often times this luck comes in the form of a companion. Take, for example, the first exoplanet detected due to its orbit around a pulsar — a rapidly spinning neutron star.

A team of researchers using the National Radio Astronomy Observatory’s Green Bank Telescope and the Very Long Baseline Array (VLBA), as well as other observatories have repeated the story, detecting an object in orbit around a distant pulsar. Except this time it’s the coldest, faintest white dwarf ever detected. So cool, in fact, its carbon has crystallized.

The punch line is this: with the help of a pulsar, astronomers have detected an Earth-size diamond in the sky.

“It’s a really remarkable object,” said lead author David Kaplan from the University of Wisconsin-Milwaukee in a press release. “These things should be out there, but because they are so dim they are very hard to find.”

The story begins when Dr. Jason Boyles, then a graduate student at West Virginia University, identified a pulsar, dubbed PSR J2222-0127, 900 light-years away in the constellation Aquarius.

When the core of a massive star runs out of energy, it collapses to form an incredibly dense neutron star or black hole. Bring a teaspoon of neutron star to Earth and it would outweigh Mount Everest at about a billion tons. A pulsar is simply a spinning neutron star.

But as a pulsar spins, lighthouse-like beams of radio waves stream from the poles of its powerful magnetic field. If they sweep past the Earth, they’ll give rise to blips of radio waves, so regular that you could set your watch by them. But if the pulsar carries a companion in tow, the tiny gravitational tugs can offset that timing slightly.

The first observations of PSR J2222-0137 identified that it was spinning more than 30 times each second. It was then observed over a two-year period with the VLBA. By applying Einstein’s theory of relativity — which predicts that light slows in the presence of a gravitational field — the researchers studied how the gravity of the companion warped space, causing delays in the radio signal as the pulsar passed behind it.

The delayed travel times helped the researchers determine the individual masses of the two stars. The pulsar has a mass of 1.2 times that of the Sun and the companion a mass 1.05 times that of the Sun. Previously, researchers had thought the companion was likely another neutron star, or a white dwarf, the remnant of a Sun-like star.

But the timing variations made the neutron star scenario unlikely. The orbits were too orderly for a second supernova to have taken place. So knowing the typical brightness of a white dwarf and its distance, astronomers initially thought they would be able to detect the elusive companion in optical and infrared light.

An image taken in visible light at the SOAR telescope of the field of the pulsar/white dwarf pair. There is no evidence for the white dwarf at the position of the pulsar in this deep image, indicating that the white dwarf is much fainter, and therefore cooler, than any such known object. (The two large white circles mask bright, overexposed stars.)
An image taken in visible light at the SOAR telescope of the field of the pulsar/white dwarf pair. The exact location of the white dwarf is known to a pixel. But it’s not there. Image Credit: NOAO

However, neither the Southern Astrophysical Research telescope in Chile nor the 10-meter Keck telescope in Hawaii was able to detect it.

“Our final image should show us a companion 100 times fainter than any other white dwarf orbiting a neutron star and about 10 times fainter than any known white dwarf, but we don’t see a thing,” said coauthor Bart Dunlap, a graduate student at the University of North Carolina. “If there’s a white dwarf there, and there almost certainly is, it must be extremely cold.”

The research team calculated that the white dwarf would be no more than 3,000 degrees Kelvin. At such a low temperature, the collapsed star would be largely crystallized carbon, similar to diamond.

The paper has been accepted for publication in the Astrophysical Journal and may be viewed here.

Spin! Crab Pulsar Speed Jumps Linked To Billions Of Tiny Vortices

Pulsars — those supernova leftovers that are incredibly dense and spin very fast — may change their speed due to activity of billions of vortices in the fluid beneath their surface, a new study says.

The work is based on a combination of research and modelling and looks at the Crab Nebula pulsar, which has periodic slowdowns in its rotation of at least 0.055 nanoseconds. Occasionally, the Crab and other pulsars see their spins speed up in an event called a “glitch”. Luckily for astronomers, there is a wealth of data on Crab because the Jodrell Bank Observatory in the United Kingdom looked at it almost daily for the last 29 years.

A glitch, the astronomers said in a statement, is “caused by the unpinning and displacement of vortices that connect the [pulsar’s] crust with the mixture of particles containing superfluid neutrons beneath the crust.”

“Surprisingly, no one tried to determine a lower limit to glitch size before. Many assumed that the smallest glitch would be caused by a single vortex unpinning. The smallest glitch is clearly much larger than we expected,” stated Danai Antonopoulou from the University of Amsterdam.

The astronomers added they will need more observations of other pulsars to better understand the results.

You can read the paper at the Monthly Notices of the Royal Astronomical Society or in preprint version on Arxiv. The research was led by C.M. Espinoza of the University of Manchester and Chile’s Pontifical Catholic University.

Source: NOVA

Runaway Pulsar Produces Longest Jet Trail Ever Observed

One of the fastest-moving pulsars ever observed is spewing out a record-breaking jet of high-energy particles that stretches 37 light years in length – the longest object in the Milky Way galaxy.

“We’ve never seen an object that moves this fast and also produces a jet,” said Lucia Pavan of the University of Geneva in Switzerland and lead author of a paper analyzing the object. “By comparison, this jet is almost 10 times longer than the distance between the sun and our nearest star.”

The pulsar, a type of neutron star, is has the official moniker of IGR J11014-6103, but is also known as the “Lighthouse nebula.” Astronomers say the pulsar’s corkscrew-like trajectory can likely be traced back to its birth in the collapse and subsequent explosion of a massive star. The curly-cue pattern in the trail suggests the pulsar is wobbling like a spinning top.

The team says that their findings suggest that “jets are common to rotation-powered pulsars, and demonstrate that supernovae can impart high kick velocities to misaligned spinning neutron stars, possibly through distinct, exotic, core-collapse mechanisms.”

The object was first seen by the European Space Agency satellite INTEGRAL. The pulsar is located about 60 light-years away from the center of the supernova remnant SNR MSH 11-61A in the constellation of Carina. Its implied speed is between 4 – 8 million km/hr (2.5 million and 5 million mph), making it one of the fastest pulsars ever observed.

IGR J11014-6103 also is producing a cocoon of high-energy particles that enshrouds and trails behind it in a comet-like tail. This structure, called a pulsar wind nebula, has been observed before, but the Chandra data show the long jet and the pulsar wind nebula are almost perpendicular to one another.

Usually, the spin axis and jets of a pulsar point in the same direction as they are moving.

“We can see this pulsar is moving directly away from the center of the supernova remnant based on the shape and direction of the pulsar wind nebula,” said co-author Pol Bordas, from the University of Tuebingen in Germany. “The question is, why is the jet pointing off in this other direction?”

One possibility requires an extremely fast rotation speed for the iron core of the star that exploded. A problem with this scenario is that such fast speeds are not commonly expected to be achievable.

“With the pulsar moving one way and the jet going another, this gives us clues that exotic physics can occur when some stars collapse,” said co-author Gerd Puehlhofer also of the University of Tuebingen.

Read the team’s paper.

Source: Chandra

This Neutron Star Behaves Just Like The Hulk

When Bruce Banner gets angry, he gets big and green and strong and well, vengeful. The Hulk is the stuff of comic book legend and as Mark Ruffalo recently showed us in The Avengers, Banner’s/Hulk’s personality can transform on a dime.

Turns out rapid transformations are the case in astronomy, too! Scientists found a peculiar neutron star that can change from radio pulsar, to X-ray pulsar, back and forth. In the Hulk’s case, a big dose of gamma rays likely fuelled his ability to transform. This star’s superpowers, however, likely come from a companion star.

“What we’re seeing is a star that is the cosmic equivalent of ‘Dr. Jekyll and Mr. Hyde,’ with the ability to change from one form to its more intense counterpart with startling speed,” stated Scott Ransom, an astronomer at the National Radio Astronomy Observatory.

“Though we have known that X-ray binaries — some of which are observed as X-ray pulsars — can evolve over millions of years to become rapidly spinning radio pulsars, we were surprised to find one that seemed to swing so quickly between the two.”

A neutron star and its companion flipping between accretion (when it emits X-rays) and when accretion has stopped (when it emits radio pulses). Credit: Bill Saxton; NRAO/AUI/NSF. Animation by Elizabeth Howell
A neutron star and its companion flipping between accretion (when it emits X-rays) and when accretion has stopped (when it emits radio pulses). Credit: Bill Saxton; NRAO/AUI/NSF. Animation by Elizabeth Howell

The star’s double personality came to light after astronomers made an accidental double-discovery. IGR J18245-2452, as the star is called, was flagged as a millisecond radio pulsar in 2005 using the  National Science Foundation’s Robert C. Byrd Green Bank Telescope. Then this year, another team found an X-ray pulsar in the same region of the star cluster M28.

It took a little while to sort out the confusion, we’re sure, but eventually astronomers realized it was the same object behaving differently. That said, they were mighty confused: “This was particularly intriguing because radio pulses don’t come from an X-ray binary and the X-ray source has to be long gone before radio signals can emerge,” stated lead researcher Alessandro Papitto, who is with of Institute of Space Sciences in Catalunya (Institut d’Estudis Espacials de Catalunya) in Spain.

The key, it turns out, comes from the interplay with the star’s companion. Material doesn’t flow continuously, as astronomers previously believed is true of these system types, but in bunches. Starting and stopping the flow then led to swings in the behavior, making the star alternate between X-ray and radio emissions.

So to sum up what is happening:

– Neutron stars like IGR J18245-2452 are superdense star remnants that formed after supernovas. A teaspoon of this material is often cited as being as heavy as a mountain (but be careful, as mass and weight are different). Still, we can all understand this stuff is very dense and would take a superhero (Hulk?) to move.

– A neutron star that has a normal star nearby forms an X-ray binary, which happens when the neutron star poaches starstuff off its companion. When the material hits the neutron star, the stuff gets really hot and emits X-rays.

– When the material stops, magnetic fields on the neutron produce radio waves. These appear to blink on and off from the perspective of Earth, as the neutron rotates super-fast (several times a second).

Pulsar diagram (© Mark Garlick)
Pulsar diagram (© Mark Garlick)

In the case of IGR J18245-2452, it behaved like an X-ray binary star for about a month, stopped suddenly, and then sent out radio waves for a while before flipping back again. (A month is less than a blink in astronomical terms, when you recall the universe is 13.8 billion years old.)

To take the longer view, astronomers used to believe that X-ray binaries could evolve into radio emitters over time. Now, though, it appears a star can be these two things at almost the same time.

“During periods when the mass flow is less intense, the magnetic field sweeps away the gas and prevents it from reaching the surface and creating X-ray emission,” NASA stated. “With the region around the neutron star relatively gas free, radio signals can easily escape and astronomers detect a radio pulsar.”

A whole suite of telescopes in Earth and space contributed to this discovery, but of note: the X-ray source was first spotted with the International Gamma-Ray Astrophysics Laboratory (INTEGRAL). You can read more details in the paper published in Nature.

Sources: National Radio Astronomy Observatory and NASA

Weekly Space Hangout – Aug. 16, 2013

Like your space news, but you just can’t handle reading any more? Then watch our Weekly Space Hangout, where we give you a rundown of all the big space news stories that broke this week.

Host: Fraser Cain

Panel: Brian Koberlein, David Dickinson, Nancy Atkinson, Nicole Gugliucci

Stories:
CIA Comes Clean About Area 51
Elon Musk’s Hyperloop
Space Fence Shut Down
Magnetar Discovered Near the Galactic Core
IAU Updates Their Naming Policy
Bright Nova in Delphinus

We record the Weekly Space Hangout every Friday at 12 pm Pacific / 3 pm Eastern as a live Google+ Hangout on Air. Join us live on YouTube, or you can listen to the audio after the fact on the 365 Days of Astronomy Podcast.

Weekly Space Hangout – April 26, 2013

We had an action packed Weekly Space Hangout on Friday, with a vast collection of different stories in astronomy and spaceflight. This week’s panel included Alan Boyle, Dr. Nicole Gugliucci, Scott Lewis, Jason Major, and Dr. Matthew Francis. Hosted by Fraser Cain.

Some of the stories we covered included: Pulsar Provides Confirmation of General Relativity, Meteorites Crashing into Saturn’s Rings, Radio Observations of Betelgeuse, Progress Docks with the ISS, Hubble Observes Comet ISON, Grasshopper Jumps 250 Meters, April 25th Lunar Eclipse, and the Mars One Reality Show.

We record the Weekly Space Hangout every Friday at 12 pm Pacific / 3 pm Eastern. You can watch us live on Google+, Cosmoquest or listen after as part of the Astronomy Cast podcast feed (audio only).