Welcome, come in to the 513th Carnival of Space! The Carnival is a community of space science and astronomy writers and bloggers, who submit their best work each week for your benefit. I’m Susie Murph, part of the team at Universe Today and CosmoQuest. So now, on to this week’s stories! Continue reading “Carnival of Space #513”
Does a distant black hole provide a new definition of pain and suffering?
The black hole, named XJ1500+0154, appears to be the real-life equivalent of the Pit of Carkoon, the nesting place of the all-powerful Sarlacc in Star Wars, which slowly digested its victims.
Over ten years ago, this giant black hole ripped apart a star and has since continued a very long lunch, feasting on the stars’ remains. Astronomers have been carefully monitoring this slow ‘digestion,’ because it is so unusual for what are called tidal disruption events (TDEs), where tidal forces from black holes tear stars apart.
“We have witnessed a star’s spectacular and prolonged demise,” said Dacheng Lin from the University of New Hampshire in Durham, New Hampshire, who led the observations of this event. “Dozens of tidal disruption events have been detected since the 1990s, but none that remained bright for nearly as long as this one.”
This decade-long feast has gone on ten times longer than any other observed TDE.
XJ1500+0154 is located in a small galaxy about 1.8 billion light years from Earth, and three telescopes have been monitoring this X-ray event: the Chandra X-ray Observatory, the Swift satellite, and the XMM-Newton.
TDEs are different from another, more common black-hole related source of X-rays in the galaxy, active galactic nuclei (AGN). Like the digestion of the Sarlacc, AGNs really can last for thousands of years. These are supermassive black holes at the center of galaxies that pull in surrounding gas and “emit copious amounts of radiation, including X-rays,” explained Lin in a blog post on the Chandra website. “Radiation from AGNs do not vary a lot because the gas surrounding them extends over a large scale and can last for tens of thousands of years.”
In contrast, TDEs are relatively short-lived, lasting only a few months. During a TDE, some of the stellar debris is flung outward at high speeds, while the rest falls toward the black hole. As it travels inwards to be consumed by the black hole, the material heats up to millions of degrees, generating a distinct X-ray flare.
XJ1500+0154 has provided an extraordinarily long, bright phase, spanning over ten years. Lin and his team said one explanation could be the most massive star ever to be completely torn apart during a TDE.
“To have the event last so long at such high luminosity requires full disruption of a relatively massive star, about twice the mass of the sun,” Lin wrote; however, “disruption of such massive stars by the SMBH is very unlikely because stars this massive are rare in most galaxies, unless the galaxy is young and actively forming stars, as in our case.
So, another more likely explanation is that this is the first TDE observed where a smaller star was completely torn apart.
Lin also said this event has broad implications for black hole physics.
“To fully explain the super-long duration of our event requires the application of recent theoretical progress on the study of TDEs,” he wrote. “In the last two years, several groups independently found that it can take a long time after the disruption of the star for the stellar debris to settle onto the accretion disk and into the SMBH. Therefore, the event can evolve much more slowly than previously thought.”
Additionally, the X-ray data also indicate that radiation from material surrounding this black hole has consistently surpassed what is called the Eddington limit, which is defined as a balance between the outward pressure of radiation from the hot gas and the inward pull of the gravity of the black hole.
Seeing evidence of such rapid growth may help astronomers understand how supermassive black holes were able to reach masses about a billion times higher than the sun when the universe was only about a billion years old.
“This event shows that black holes really can grow at extraordinarily high rates,” said co-author Stefanie Komossa of QianNan Normal University for Nationalities in Duyun City, China. “This may help understand how precocious black holes came to be.”
Lin and his team will continue to monitor this event, and they expect the X-ray brightness to fade over the next few years, meaning the supply of ‘food’ for this long lunch will soon be consumed.
The Earthly Northern Lights are beautiful and astounding, but when it comes to planetary light shows, what happened at Jupiter in 2011 might take the cake. In 2011, a coronal mass ejection (CME) struck Jupiter, producing x-ray auroras 8 times brighter than normal, and hundreds of times more energetic than Earth’s auroras. A paper in the March 22nd, 2016 issue of the Journal of Geophysical Research gave the details.
The Sun emits a ceaseless stream of energetic particles called the solar wind. Sometimes, the Sun ramps up its output, and what is called a coronal mass ejection occurs. A coronal mass ejection is a massive burst of matter and electromagnetic radiation. Though they’re slow compared to other phenomena arising from the Sun, such as solar flares, CMEs are extremely powerful.
When the CME in 2011 reached Jupiter, NASA’s Chandra X-Ray Observatory was watching, the first time that Jupiter’s X-ray auroras were monitored at the same time that a CME arrived. Along with some very interesting images of the event, the team behind the study learned other things. The CME that struck Jupiter actually compressed that planet’s magnetosphere. It forced the boundary between the solar wind and Jupiter’s magnetic field in towards the planet by more than 1.6 million kilometers (1 million miles.)
The scientists behind this study used the data from this event to not only pinpoint the source of the x-rays, but also to identify areas for follow-up investigation. They’ll be using not only Chandra, but also the European Space Agency’s XMM Newton observatory to collect data on Jupiter’s magnetic field, magnetosphere, and aurora.
NASA’s Juno spacecraft will reach Jupiter this summer. One of its primary missions is to map Jupiter’s magnetic fields, and to study the magnetosphere and auroras. Juno’s results will be fascinating to anyone interested in Jupiter’s auroras.
Here at Universe Today we’ve written about Jupiter’s aurora’s here, coronal mass ejections here, and the Juno mission here.
Host: Fraser Cain (@fcain) Special Guest:Andy Weir , author of “The Martian”
Andy was first hired as a programmer for a national laboratory at age fifteen and has been working as a software engineer ever since. He is also a lifelong space nerd and a devoted hobbyist of subjects like relativistic physics, orbital mechanics, and the history of manned spaceflight. “The Martian” is his first novel.
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 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.
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.
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.
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.
Hot young stars are wildly active, emitting huge eruptions of charged particles form their surfaces. But as they age they naturally become less active, their X-ray emission weakens and their rotation slows.
Astronomers have theorized that a hot Jupiter — a sizzling gas giant circling close to its host star — might be able to sustain a young star’s activity, ultimately prolonging its youth. Earlier this year, two astronomers from the Harvard-Smithsonian Center for Astrophysics tested this hypothesis and found it true.
But now, observations of a different system show the opposite effect: a planet that’s causing its star to age much more quickly.
The planet, WASP-18b has a mass roughly 10 times Jupiter’s and circles its host star in less than 23 hours. So it’s not exactly a classic hot Jupiter — a sizzling gas giant whipping around its host star — because it’s characteristics are a little more drastic.
“WASP-18b is an extreme exoplanet,” said lead author Ignazio Pillitteri of the National Institute for Astrophysics in Italy, in a news release. “It is one of the most massive hot Jupiters known and one of the closest to its host star, and these characteristics lead to unexpected behavior.”
The team thinks WASP-18 is 600 million years old, relatively young compared to our 5-billion-year-old Sun. But when Pillitteri and colleagues took a long look with NASA’s Chandra X-ray Observatory at the star, they didn’t see any X-rays — a telltale sign the star is youthful. In fact, the observations show the star is 100 times less active than it should be.
“We think the planet is aging the star by wreaking havoc on its innards,” said co-author Scott Wolk (who also worked on the previous study showing the opposite effect) from the Harvard-Smithsonian Center for Astrophysics.
The researchers argue that tidal forces created by the gravitational pull of the massive planet might have disrupted the star’s magnetic field generated by the motion of conductive plasma deep inside the star. It’s possible the exoplanet significantly interfered with the upper layers of the convective zone, reduced any mixing of stellar material, and effectively canceled out the magnetic activity.
The effect of tidal forces from the planet may also explain an unusually high amount of lithium seen in the star. Lithium is usually abundant in younger stars, but disappears over time as convection carries it further toward the star’s center, where it’s destroyed by nuclear reactions. So if there’s less convection — as seems to be the case for WASP 18 — then the lithium won’t circulate toward the center of the star and instead will survive.
The findings have been published in the July issue of Astronomy and Astrophysics and are available online.
Could a strange X-ray signal coming from the Perseus galaxy cluster be a hint of the elusive dark matter in our Universe?
Using archival data from the Chandra X-ray Observatory and the XMM-Newton mission, astronomers found an unidentified X-ray emission line, or a spike of intensity at a very specific wavelength of X-ray light. This spike was also found in 73 other galaxy clusters in XMM-Newton data.
The scientists propose that one intriguing possibility is that the X-rays are produced by the decay of sterile neutrinos, a hypothetical type of neutrino that has been proposed as a candidate for dark matter and is predicted to interact with normal matter only via gravity.
“We know that the dark matter explanation is a long shot, but the pay-off would be huge if we’re right,” said Esra Bulbul of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, who led the study. “So we’re going to keep testing this interpretation and see where it takes us.”
Astronomers estimate that roughly 85 percent of all matter in the Universe is dark matter, invisible to even the most powerful telescopes, but detectable by its gravitational pull.
Galaxy clusters are good places to look for dark matter. They contain hundreds of galaxies as well as a huge amount of hot gas filling the space between them. But measurements of the gravitational influence of galaxy clusters show that the galaxies and gas make up only about one-fifth of the total mass. The rest is thought to be dark matter.
Bulbul explained in a post on the Chandra blog that she wanted try hunting for dark matter by “stacking” (layering observations on top of each other) large numbers of observations of galaxy clusters to improve the sensitivity of the data coming from Chandra and XMM-Newton.
“The great advantage of stacking observations is not only an increased signal-to-noise ratio (that is, the amount of useful signal compared to background noise), but also the diminished effects of detector and background features,” wrote Bulbul. “The X-ray background emission and instrumental noise are the main obstacles in the analysis of faint objects, such as galaxy clusters.”
Her primary goal in using the stacking technique was to refine previous upper limits on the properties of dark matter particles and perhaps even find a weak emission line from previously undetected metals.
“These weak emission lines from metals originate from the known atomic transitions taking place in the hot atmospheres of galaxy clusters,” said Bulbul. “After spending a year reducing, carefully examining, and stacking the XMM-Newton X-ray observations of 73 galaxy clusters, I noticed an unexpected emission line at about 3.56 kiloelectron volts (keV), a specific energy in the X-ray range.”
In theory, a sterile neutrino decays into an active neutrino by emitting an X-ray photon in the keV range, which can be detectable through X-ray spectroscopy. Bulbul said that her team’s results are consistent with the theoretical expectations and the upper limits placed by previous X-ray searches.
Bulbul and her colleagues worked for a year to confirm the existence of the line in different subsamples, but they say they still have much work to do to confirm that they’ve actually detected sterile neutrinos.
“Our next step is to combine data from Chandra and JAXA’s Suzaku mission for a large number of galaxy clusters to see if we find the same X-ray signal,” said co-author Adam Foster, also of CfA. “There are lots of ideas out there about what these data could represent. We may not know for certain until Astro-H launches, with a new type of X-ray detector that will be able to measure the line with more precision than currently possible.”
Astro-H is another Japanese mission scheduled to launch in 2015 with a high-resolution instrument that should be able to see better detail in the spectra, and Bulbul said they hope to be able to “unambiguously distinguish an astrophysical line from a dark matter signal and tell us what this new X-ray emission truly is.”
Since the emission line is weak, this detection is pushing the capabilities Chandra and XMM Newton in terms of sensitivity. Also, the team says there may be explanations other than sterile neutrinos if this X-ray emission line is deemed to be real. There are ways that normal matter in the cluster could have produced the line, although the team’s analysis suggested that all of these would involve unlikely changes to our understanding of physical conditions in the galaxy cluster or the details of the atomic physics of extremely hot gases.
The authors also note that even if the sterile neutrino interpretation is correct, their detection does not necessarily imply that all of dark matter is composed of these particles.
The Chandra press release shared an interesting behind-the-scenes look into how science is shared and discussed among scientists:
Because of the tantalizing potential of these results, after submitting to The Astrophysical Journal the authors posted a copy of the paper to a publicly accessible database, arXiv. This forum allows scientists to examine a paper prior to its acceptance into a peer-reviewed journal. The paper ignited a flurry of activity, with 55 new papers having already cited this work, mostly involving theories discussing the emission line as possible evidence for dark matter. Some of the papers explore the sterile neutrino interpretation, but others suggest different types of candidate dark matter particles, such as the axion, may have been detected.
Only a week after Bulbul et al. placed their paper on the arXiv, a different group, led by Alexey Boyarsky of Leiden University in the Netherlands, placed a paper on the arXiv reporting evidence for an emission line at the same energy in XMM-Newton observations of the galaxy M31 and the outskirts of the Perseus cluster. This strengthens the evidence that the emission line is real and not an instrumental artifact.
Supernovas are some of the most energetic and powerful events in the observable Universe. Briefly outshining entire galaxies, they are the final, dying outbursts of stars several times more massive than our Sun. And while we know supernovas are responsible for creating the heavy elements necessary for everything from planets to people to power tools, scientists have long struggled to determine the mechanics behind the sudden collapse and subsequent explosion of massive stars.
Now, thanks to NASA’s NuSTAR mission, we have our first solid clues to what happens before a star goes “boom.”
The image above shows the supernova remnant Cassiopeia A (or Cas A for short) with NuSTAR data in blue and observations from the Chandra X-ray Observatory in red, green, and yellow. It’s the shockwave left over from the explosion of a star about 15 to 25 times more massive than our Sun over 330 years ago*, and it glows in various wavelengths of light depending on the temperatures and types of elements present.
Previous observations with Chandra revealed x-ray emissions from expanding shells and filaments of hot iron-rich gas in Cas A, but they couldn’t peer deep enough to get a better idea of what’s inside the structure. It wasn’t until NASA’s Nuclear Spectroscopic Telescope Array — that’s NuSTAR to those in the know — turned its x-ray vision on Cas A that the missing puzzle pieces could be found.
And they’re made of radioactive titanium.
Many models have been made (using millions of hours of supercomputer time) to try to explain core-collapse supernovas. One of the leading ones has the star ripped apart by powerful jets firing from its poles — something that’s associated with even more powerful (but focused) gamma-ray bursts. But it didn’t appear that jets were the cause with Cas A, which doesn’t exhibit elemental remains within its jet structures… and besides, the models relying on jets alone didn’t always result in a full-blown supernova.
As it turns out, the presence of asymmetric clumps of radioactive titanium deep within the shells of Cas A, revealed in high-energy x-rays by NuSTAR, point to a surprisingly different process at play: a “sloshing” of material within the progenitor star that kickstarts a shockwave, ultimately tearing it apart.
Watch an animation of how this process occurs:
The sloshing, which occurs over a time span of a mere couple hundred milliseconds — literally in the blink of an eye — is likened to boiling water on a stove. When the bubbles break through the surface, the steam erupts.
Only in this case the eruption leads to the insanely powerful detonation of an entire star, blasting a shockwave of high-energy particles into the interstellar medium and scattering a periodic tableful of heavy elements into the galaxy.
In the case of Cas A, titanium-44 was ejected, in clumps that echo the shape of the original sloshing asymmetry. NuSTAR was able to image and map the titanium, which glows in x-ray because of its radioactivity (and not because it’s heated by expanding shockwaves, like other lighter elements visible to Chandra.)
“Until we had NuSTAR we couldn’t really see down into the core of the explosion,” said Caltech astronomer Brian Grefenstette during a NASA teleconference on Feb. 19.
“Previously, it was hard to interpret what was going on in Cas A because the material that we could see only glows in X-rays when it’s heated up. Now that we can see the radioactive material, which glows in X-rays no matter what, we are getting a more complete picture of what was going on at the core of the explosion.”
– Brian Grefenstette, lead author, Caltech
Okay, so great, you say. NASA’s NuSTAR has found the glow of titanium in the leftovers of a blown-up star, Chandra saw some iron, and we know it sloshed and ‘boiled’ a fraction of a second before it exploded. So what?
“Now you should care about this,” said astronomer Robert Kirshner of the Harvard-Smithsonian Center for Astrophysics. “Supernovae make the chemical elements, so if you bought an American car, it wasn’t made in Detroit two years ago; the iron atoms in that steel were manufactured in an ancient supernova explosion that took place five billion years ago. And NuSTAR shows that the titanium that’s in your Uncle Jack’s replacement hip were made in that explosion too.
“We’re all stardust, and NuSTAR is showing us where we came from. Including our replacement parts. So you should care about this… and so should your Uncle Jack.”
And it’s not just core-collapse supernovas that NuSTAR will be able to investigate. Other types of supernovas will be scrutinized too — in the case of SN2014J, a Type Ia that was spotted in M82 in January, even right after they occur.
“We know that those are a type of white dwarf star that detonates,” NuSTAR principal investigator Fiona Harrison responded to Universe Today during the teleconference. “This is very exciting news… NuSTAR has been looking at [SN2014J] for weeks, and we hope to be able to say something about that explosion as well.”
One of the most valuable achievements of the recent NuSTAR findings is having a new set of observed constraints to place on future models of core-collapse supernovas… which will help provide answers — and likely new questions — about how stars explode, even hundreds or thousands of years after they do.
“NuSTAR is pioneering science, and you have to expect that when you get new results, it’ll open up as many questions as you answer,” said Kirshner.
Launched in June of 2012, NuSTAR is the first focusing hard X-ray telescope to orbit Earth and the first telescope capable of producing maps of radioactive elements in supernova remnants.