A new composite of NGC 4258 features X-rays from Chandra (blue), radio waves from the VLA (purple), optical data from Hubble (yellow and blue), and infrared with Spitzer (red). Image Credit: Chandra
While Fourth of July festivities tonight may bring brilliant colors blazing across the night sky, only 23 million light-years away is another immense cosmic display, complete with a supermassive black hole, shock waves, and vast reservoirs of gas.
The night sky never ceases to amaze. And NGC 4258, also known as Messier 106, is a sight to be seen. A new image from NASA’s Chandra X-ray Observatory is shedding light on one of the galaxy’s most startling features: instead of two spiral arms, typical for any massive spiral galaxy, it appears to have four (imaged above in blue and purple).
Although the second pair of arms can be seen in visible light images as ghostly wisps of gas, they are prominent in images outside the visible spectrum, such as those using X-ray or radio waves. Unlike normal arms, they are made up of hot gas rather than stars, and their origin has remained a mystery.
Astronomers now think the arms — so-called anomalous for their atypical features — are indirectly caused by the supermassive black hole at NGC 4258’s heart.
Images from multiple telescopes help paint a complete picture. Radio data taken with the Very Large Array show that the supermassive black hole is producing powerful jets. As these jets travel through the galactic matter, they disrupt the surrounding gas and generate shock waves. These shock waves, seen by NASA’s Spitzer Space Telescope, heat the anomalous arms — composed of reservoirs of gas as massive as about 10 million Suns — to thousands of degrees.
Finally, the recent Chandra X-ray image also reveals huge bubbles of hot gas above and below the plane of the galaxy. These bubbles indicate that although much of the gas was originally in the disk of the galaxy, it was heated to such high temperatures that it was ejected into the outer regions by the jets from the supermassive black hole.
The results provide drastic implications for the fate of the galaxy. Most of the gas in the disk of the galaxy has been ejected, causing stars to form at a rate ten times slower than the Milky Way. Further, astronomers estimate that all of the remaining gas will be ejected within the next 300 million years.
Although NGC 4258 is currently a sight to be seen in any small telescope, like the best fireworks display followed by smoke, its death is inescapable.
The results were published in The Astrophysical Journal Letters and are available online.
A mysterious X-ray signal in the Perseus galaxy cluster. Credit: NASA/CXC/SAO/E.Bulbul, et al.
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.
The Whirlpool galaxy seen in both optical and X-ray light. Image Credit: X-ray: NASA/CXC/Wesleyan Univ./R.Kilgard, et al; Optical: NASA/STScI
In any galaxy there are hundreds of X-ray binaries: systems consisting of a black hole capturing and heating material from a relatively low-mass orbiting companion star. But high-mass X-ray binaries — systems consisting of a black hole and an extremely high-mass companion star — are hard to come by. In the Milky Way there’s only one: Cygnus X-1. But 30 million light-years away in the Whirlpool galaxy, M51, there are a full 10 high-mass X-ray binaries.
Nearly a million seconds of observing time with NASA’s Chandra X-ray Observatory has revealed these specks. “This is the deepest, high-resolution exposure of the full disk of any spiral galaxy that’s ever been taken in the X-ray,” said Roy Kilgard, from Wesleyan University, at a talk presented at the American Astronomical Society meeting today in Boston. “It’s a remarkably rich data set.”
Within the image there are 450 X-ray points of light, 10 of which are likely X-ray binaries.
The Whilpool galaxy is thought to have so many X-ray binaries because it’s in the process of colliding with a smaller companion galaxy. This interaction triggers waves of star formation, creating new stars at a rate seven times faster than the Milky Way and supernova deaths at a rate 10-100 times faster. The more-massive stars simply race through their evolution in a few million years and collapse to form neutron stars or black holes quickly.
“In this image, there’s a very strong correlation between the fuzzy purple stuff, which is hot gas in the X-ray, and the fuzzy red stuff, which is hydrogen gas in the optical,” said Kilgard. “Both of these are tracing the star formation very actively. You can see it really enhanced in the northern arm that approaches the companion galaxy.”
Eight of the 10 X-ray binaries are located close to star forming regions.
Chandra is providing astronomers with an in depth look at a class of objects that has only one example in the Milky Way.
“We’re catching them at a short window in their evolutionary cycle,” said Kilgard. “The massive star that formed the black hole has died, and the massive star that is accreting material onto the black hole has not yet died. The window at which these objects are X-ray bright is really short. It’s maybe only tens of thousands of years.”
Galaxy clusters MACS J0717+3745 colliding about five billion light-years away from Earth. This is a composite image of visible light from the Hubble Space Telescope (background), X-ray data from the Chandra X-Ray Observatory (blue) and radio waves from the Very Large Array (red).Credit: Van Weeren, et al.; Bill Saxton, NRAO/AUI/NSF; NASA
Shock waves! Fast-moving particles! Magnetic fields! This image has it all. Behold the merging galaxy clusters MACS J0717+3745 about five billion light-years from our planet.
That funny red thing you see in the center is new data from the Karl G. Jansky Very Large Array showing a spot where “shocks caused by the collisions are accelerating particles that then interact with magnetic fields and emit the radio waves,” officials at the National Radio Astronomical Observatory stated.
“The complex shape of this region is unique; we’ve never spotted anything like this before,” stated Reinout van Weeren, an Einstein Fellow at the Harvard-Smithsonian Center for Astrophysics. “The shape probably is the result of the multiple ongoing collisions.”
This is a composite image of new exposures from VLA and the Chandra X-Ray Observatory, with an older image from the Hubble Space Telescope. And if you take a second look, there’s also a black hole: “The straight, elongated radio-emitting object is a foreground galaxy whose central black hole is accelerating jets of particles in two directions,” NRAO added. “The red object at bottom-left is a radio galaxy that probably is falling into the cluster.”
Astronomers presented their findings at the American Astronomical Society meeting this week in Boston.
A gas stream from galaxy ESO 137-001 shines brightly in X-rays captured by the Chandra X-Ray Observatory. The galaxy is captured in other wavelengths by the Hubble Space Telescope. Credit: NASA, ESA, CXC
Is that a tractor beam trying to latch on to galaxy ESO 137-001? While the bold blue stripe in the picture above looks like a Star Trek-like technology, this new picture combination captures a stream of gas shining brightly in X-rays.
The “galactic disrobing” is taking place as the galaxy moves through the center of a star cluster full of superheated gas, scientists said. You can see another shot of the chaos below the jump.
From Earth’s perspective, the galaxy (which looks a little like a jellyfish) is found in the Triangulum Australe (The Southern Triangle) , and is part of the Norma Cluster that is about 200 million light-years from the Milky Way (our own galaxy). ESO 137-001 is moving through a galaxy cluster called Abell 3627. All of the superheated gas in this region is making ESO 137-001 bleed gas from its own structure as it goes.
“These streaks are actually hot young stars, encased in wispy streams of gas that are being torn away from the galaxy by its surroundings as it moves through space,” stated the Hubble European Space Agency Information Centre. “This violent galactic disrobing is due to a process known as ram pressure stripping — a drag force felt by an object moving through a fluid. The fluid in question here is superheated gas, which lurks at the centres of galaxy clusters.”
“This image also shows other telltale signs of this process, such as the curved appearance of the disc of gas and dust — a result of the forces exerted by the heated gas,” the centre added. “The cluster’s drag may be strong enough to bend ESO 137-001, but in this cosmic tug-of-war the galaxy’s gravitational pull is strong enough to hold on to the majority of its dust — although some brown streaks of dust displaced by the stripping are visible.”
This stripping has been caught in other images, such as these 2007 and 2010 pictures from the Chandra X-Ray Observatory.
A Hubble Space Telescope image of spiral galaxy ESO 137-001 moving through galaxy cluster Abell 3627. The tendrils (visible in ultraviolet light) are gas flowing away from the galaxy as it moves through superheated gas in the area. Credit: NASA, ESA
Multi-wavelength view of the elliptical galaxy NGC 5044. Credit: Digitised Sky Survey/NASA Chandra/Southern Observatory for Astrophysical Research/Very Large Array (Robert Dunn et al. 2010)
Contradicting past theories, cold gas has been found in abundance in some elliptical galaxies — showing that there must be some other explanation why these types of galaxies don’t form new stars. Astronomers believe that the jets from supermassive black holes in these galaxies’ center must push around the gas and prevent stars from forming.
Researchers spotted the gas for the first time using old data from the recently retired Herschel space observatory, which was able to peer well into the infrared — where it spotted carbon ions and oxygen atoms. This find stands against the previous belief that these galaxies were “red and dead”, referring to their physical appearance and the fact that they form no new stars.
“We looked at eight giant elliptical galaxies that nobody had looked at with Herschel before and we were delighted to find that, contrary to previous belief, six out of eight abound with cold gas”, stated Norbert Werner, a researcher at Stanford University in California who led the study.
“These galaxies are red, but with the giant black holes pumping in their hearts, they are definitely not dead,” added Werner.
NGC 1399, an elliptical galaxy about 65 million light years from Earth. Credit: NASA, Chandra
Previously, scientists thought that the galaxies got rid of their cold gas or had used it all up during a burst of earlier star formation. With cold gas found in the majority of the sample, researchers then used other observatories to try to find warmer gas up to tens of millions of Kelvin (or Fahrenheit or Celsius).
X-ray information from NASA’s Chandra X-ray Observatory revealed that there is hot gas cooling in six of the eight galaxies, but not in the remaining two of the sample.
“This is consistent with theoretical expectations: once cooled, the hot gas would become the warm and cold gas that are observed at longer wavelengths. However, in these galaxies the cooling process somehow stopped, and the cold gas failed to condense and form stars,” the European Space Agency stated.
“While the six galaxies with plenty of cold gas harbour moderately active black holes at their centres,” ESA added, “the other two show a marked difference. In the two galaxies without cold gas, the central black holes are accreting matter at frenzied pace, as confirmed by radio observations showing powerful jets of highly energetic particles that stem from their cores.”
An extraordinary jet trailing behind a runaway pulsar is seen in this composite image. Credit: X-ray: NASA/CXC/ISDC/L.Pavan et al, Radio: CSIRO/ATNF/ATCA Optical: 2MASS/UMass/IPAC-Caltech/NASA/NSF
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.
The "Hand ( or Fist?) of God" nebula enshrouding pulsar PSR B1509-58. The upper red cloud structure is RCW 89. The image is a composite of Chandra observations (red & green), while NuSTAR observations are denoted in blue.
One star player in this week’s findings out of the 223rd meeting of the American Astronomical Society has been the Nuclear Spectroscopic Telescope Array Mission, also known as NuSTAR. On Thursday, researchers revealed some exciting new results and images from the mission, as well as what we can expect from NuSTAR down the road.
NuSTAR was launched on June 13th, 2012 on a Pegasus XL rocket deployed from a Lockheed L-1011 “TriStar” aircraft flying near the Kwajalein Atoll in the middle of the Pacific Ocean.
Part of a new series of low-cost missions, NuSTAR is the first of its kind to employ a space telescope focusing on the high energy X-ray end of the spectrum centered around 5-80 KeV.
Daniel Stern, part of the NuSTAR team at JPL Caltech, revealed a new X-ray image of the now-famous supernova remnant dubbed “The Hand of God.” Discovered by the Einstein X-ray observatory in 1982, the Hand is home to pulsar PSR B1509-58 or B1509 for short, and sits about 18,000 light years away in the southern hemisphere constellation Circinus. B1509 spins about 7 times per second, and the supernova that formed the pulsar is estimated to have occurred 20,000 years ago and would’ve been visible form Earth about 2,000 years ago.
A diagram of the NuSTAR satellite. (NASA/JPL/Caltech)
While the Chandra X-ray observatory has scrutinized the region before, NuSTAR can peer into its very heart. In fact, Stern notes that views from NuSTAR take on less of an appearance of a “Hand” and more of a “Fist”. Of course, the appearance of any nebula is a matter of perspective. Pareidolia litter the deep sky, whether it’s the Pillars of Creation to the Owl Nebula. We can’t help but being reminded of the mysterious “cosmic hand” that the Guardians of Oa of Green Lantern fame saw when they peered back at the moment of creation. Apparently, the “Hand” is also rather Simpson-esque, sporting only three “fingers!”
An diagram of the Hand of God. Credit: NASA/JPL/Caltech/McGill).
NuSTAR is the first, and so far only, focusing hard X-ray observatory deployed in orbit. NuSTAR employs what’s known as grazing incidence optics in a Wolter telescope configuration, and the concentric shells of the detector look like layers on an onion. NuSTAR also requires a large focal length, and employs a long boom that was deployed shortly after launch.
The hard X-ray regime that NuSTAR monitors is similar to what you encounter in your dentist’s office or in a TSA body scanner. Unlike the JEM-X monitor aboard ESA’s INTERGRAL or the Swift observatory, which have a broad resolution of about half a degree to a degree, NuSTAR has an unprecedented resolution of about 18 arc seconds.
The first data release from NuSTAR was in late 2013. NuSTAR is just begging to show its stuff, however, in terms of what researchers anticipate that it’s capable of.
“NuSTAR is uniquely able to map the Titanium-44 emission, which is a radioactive tracer of (supernova) explosion physics,” Daniel Stern told Universe Today.
NuSTAR will also be able to pinpoint high energy sources at the center of our galaxy. “No previous high-energy mission has had the imaging resolution of NuSTAR,” Stern told Universe Today. ”Our order-of-magnitude increase in image sharpness means that we’re able to map out that very rich region of the sky, which is populated by supernovae remnants, X-ray binaries, as well as the big black hole at the center of our Galaxy, Sagittarius A* (pronounced “A-star).”
NuSTAR identifies new black hole candidates (in blue) in the COSMOS field. The discoveries in the image above are overlayed on previous black holes spotted by Chandra in the same field, which are denoted in red and green. (Credit-NASA/JPL-Caltech/Yale University).
Yale University researcher Francesca Civano also presented a new image from NuSTAR depicting black holes that were previously obscured from view. NuSTAR is especially suited for this, gazing into the hearts of energetic galaxies that are invisible to observatories such Chandra or XMM-Newton. The image presented covers the area of Hubble’s Cosmic Evolution Survey, known as COSMOS in the constellation Sextans. In fact, Civano notes that NuSTAR has already seen the highest number of obscured black hole candidates to date.
“This is a hot topic in astronomy,” Civano said in a recent press release. “We want to understand how black holes grew and the degree to which they are obscured.”
To this end, NuSTAR researchers are taking a stacked “wedding cake” approach, looking at successively larger slices of the sky from previous surveys. These include looking at the quarter degree field of the Great Observatories Origins Deep Survey (GOOD-S) for 18 days, the two degree wide COSMOS field for 36 days, and the large four degree Swift-BAT fields for 40 day periods hunting for serendipitous sources.
Interestingly, NuSTAR has also opened the window on the hard X-ray background that permeates the universe as well. This peaks in the 20-30 KeV range, and is the combination of the X-ray emissions of millions of black holes.
“For several decades already, we’ve known what the sum total emission of the sky is across the X-ray regime,” Stern told Universe Today. “The shape of this cosmic X-ray background peaks strongly in the NuSTAR range. The most likely interpretation is that there are a large number of obscured black holes out there, objects that are hard to find in other energy bands. NuSTAR should find these sources.”
And NuSTAR may just represent the beginning of a new era in X-ray astronomy. ESA is moving ahead with its next generation flagship X-ray mission, known as Athena+, set to launch sometime next decade. Ideas abound for wide-field imagers and X-ray polarimeters, and one day, we may see a successor to NuSTAR dubbed the High-Energy X-ray Probe or (HEX-P) make it into space.
But for now, expect some great science out of NuSTAR, as it unlocks the secrets of the X-ray universe!
A composite x-ray and optical image of a dwarf galaxy showing the x-ray transcient in the inset. Credit-CFHT (Optical), NASA/CXC/University of Alabama/GSCF/UMD/W.P. Maksym, D.Donato et al.
This week, astronomers announced the detection of a rare event, a star being torn to shreds by a massive black hole in the heart of a distant dwarf galaxy. The evidence was presented Wednesday January 8th at the ongoing 223rd meeting of the American Astronomical Society being held this week in Washington D.C.
Although other instances of the death of stars at the hands of black holes have been witnessed before, Chandra may have been the first to document an intermediate black hole at the heart of a dwarf galaxy “in the act”.
The results span observations carried out by the space-based Chandra X-ray observatory over a period spanning 1999 to 2005. The search is part of an archival study of observations, and revealed no further outbursts after 2005.
“We can’t see the star being torn apart by the black hole, but we can track what happens to the star’s remains,” said University of Alabama’s Peter Maksym in a recent press release. A comparison of with similar events seen in larger galaxies backs up the ruling of “death by black hole.” A competing team led by Davide Donato also looked at archival data from Chandra and the Extreme Ultraviolet Explorer (EUVE), along with supplementary observations from the Canada-France-Hawaii Telescope to determine the brightness of the host galaxy, and gained similar results.
The dwarf galaxy in the Abell 1795 cluster that was observed has the name WINGS J134849.88+263557.5, or WINGS J1348 for short. The Abell 1795 cluster is about 800 million light years distant.
WINGS denotes the galaxy’s membership in the WIde-field Nearby Galaxy-cluster Survey, and the phone number-like designation is the galaxy’s position in the sky in right ascension and declination.
Like most galaxies associated with galaxy clusters, WINGS J1348 a dwarf galaxy probably smaller than our own satellite galaxy known as the Large Magellanic Cloud. The Abell 1795 cluster is located in the constellation Boötes, and WINGS J1348 has an extremely faint visual magnitude of +22.46.
An optical view of the Abell 1795 galaxy cluster. Credit- NASA/CFHT/D. Donato et al.
“Scientists have been searching for these intermediate mass black holes for decades,” NASA’s Davide Donato said in a recent press release “We have lots of evidence for small black holes and very big ones, but these medium-sized ones have been tough to pin down.”
Maksym notes in an interview with Universe Today that this isn’t the first detection of an intermediate-mass black hole, which are a class of black holes often dubbed the “mostly” missing link between stellar mass and super massive black holes.
The mass range for intermediate black holes is generally pegged at 100 to one million solar masses.
What makes the event witnessed by Chandra in WINGS J1348 special is that astronomers managed to capture a rare tidal flare, as opposed to a supermassive black hole in the core of an active galaxy.
A closeup view of the bright, long duration flare witnessed by Chandra pre-2005. Credit- NASA/CXC/University of Alabama/W.P. Maksym et al.
“Most of the time, black holes eat very little, so they can hide very well,” Maksym said in the AAS meeting on Wednesday.
This discovery pushes the limits on what we know of intermediate black holes. By documenting an observed number of tidal flare events, it can be inferred that a number of inactive black holes must be lurking in galaxies as well. The predicted number of tidal events that occur also have implications for the eventual detection of gravity waves from said mergers.
And more examples of these types of X-ray flare events could be waiting to be uncovered in the Chandra data as well.
“Chandra has taken quite a few pictures over the past 13+ years, and collaborators and I have an ongoing program to look for more tidal flares,” Maksym told Universe Today. “We’ve found one other this way, from a larger galaxy, and hope to find more. Abell 1795 was a particularly good place to look because as a calibration source, there were tons of pictures.”
Use of Chandra data was also ideal for the study because its spatial resolution allowed researchers to pinpoint an individual galaxy in the cluster. Maksym also notes that while it’s hard to get follow-up observations of events based on archival data, future missions dedicated to X-ray astronomy with wider fields of view may be able to scour the skies looking for such tidal flaring events.
The NuSTAR satellite was the latest X-Ray observatory to launch in 2012. NASA’s Extreme Ultraviolet Explorer picked up a strong ultraviolet source in 1998 right around the time of the tidal flare event, and ESA’s XMM-Newton satellite may have detected the event in 2000 as well.
This was also one of the smallest galaxies ever observed to contain a black hole. Maksym noted in Wednesday’s press conference that an alternative explanation could be a super-massive black hole in a tiny galaxy that just “nibbled” on a passing star, but said that new data from the Gemini observatory does not support this.
“It would be like looking into a dog house and finding a large ogre crammed in there,” Maksym said at Wednesday’s press conference.
This discovery provides valuable insight into the nature of intermediate mass black holes and their formation and behavior. What other elusive cosmological beasties are lying in wait to be discovered in the archives?
Congrats to Maksym and teams on this exciting new discovery, and the witnessing of a rare celestial event!
A composite image in X-ray and radio showing a likely candidate for a jet emanating from the supermassive black hole at the center of the Milky Way. X-ray: NASA/CXC/UCLA/Z.Li et al; Radio: NRAO/VLA
Jets of high energy particles emanating from a black hole have been detected plenty of times before, but in other galaxies, that is — not from the supermassive black hole at the center of the Milky Way, known as Sagittarius A* (Sgr A*). Previous studies and other evidence suggested that perhaps there were jets – or ghosts of past jets – but many findings and studies often contradicted each other, and none were considered definitive.
Now, astronomers using Chandra X-ray Observatory and the Very Large Array (VLA) radio telescope have found strong evidence Sgr A* is producing a jet of high-energy particles.
“For decades astronomers have looked for a jet associated with the Milky Way’s black hole. Our new observations make the strongest case yet for such a jet,” said Zhiyuan Li of Nanjing University in China, lead author of a study in The Astrophysical Journal.
The supermassive black hole at the center of the Milky Way is about four million times more massive than our Sun and lies about 26,000 light-years from Earth.
While the common notion is that black holes inhale and ingest everything that comes their way, that’s not always true. Sometimes they reject small portions of incoming mass, pushing it away in the form of a powerful jet, and many times a pair of jets. These jets also feed the surroundings, releasing both mass and energy and likely play important roles in regulating the rate of formation of new stars.
Sgr A* is presently known to be consuming very little material, and so the jet is weak, making it difficult to detect. Astronomers don’t see another jet “shooting” in the opposite direction but that may be because of gas or dust blocking the line of sight from Earth or a lack of material to fuel the jet. Or there may be just a single jet.
“We were very eager to find a jet from Sgr A* because it tells us the direction of the black hole’s spin axis. This gives us important clues about the growth history of the black hole,” said Mark Morris of the University of California at Los Angeles, a co-author of the study.
The study shows the spin axis of Sgr A* is pointing in one direction, parallel to the rotation axis of the Milky Way, which indicates to astronomers that gas and dust have migrated steadily into Sgr A* over the past 10 billion years. If the Milky Way had collided with large galaxies in the recent past and their central black holes had merged with Sgr A*, the jet could point in any direction.
The jet appears to be running into gas near Sgr A*, producing X-rays detected by Chandra and radio emission observed by the VLA. The two key pieces of evidence for the jet are a straight line of X-ray emitting gas that points toward Sgr A* and a shock front — similar to a sonic boom — seen in radio data, where the jet appears to be striking the gas. Additionally, the energy signature, or spectrum, in X-rays of Sgr A* resembles that of jets coming from supermassive black holes in other galaxies.
The Chandra observations in this study were taken between September 1999 and March 2011, with a total exposure of about 17 days.
