In 1916, Albert Einstein put the finishing touches on his Theory of General Relativity, a journey that began in 1905 with his attempts to reconcile Newton’s own theories of gravitation with the laws of electromagnetism. Once complete, Einstein’s theory provided a unified description of gravity as a geometric property of the cosmos, where massive objects alter the curvature of spacetime, affecting everything around them.
What’s more, Einstein’s field equations predicted the existence of black holes, objects so massive that even light cannot escape their surfaces. GR also predicts that black holes will bend light in their vicinity, an effect that can be used by astronomers to observe more distant objects. Relying on this technique, an international team of scientists made an unprecedented feat by observing light caused by an X-ray flare that took place behind a black hole.
Auroras come in many shapes and sizes. Jupiter is well known for its spectacular complement of bright polar lights, which also have the distinction of appearing in the X-ray band. These auroras are also extreme power sources, emitting almost a gigawatt of energy in a few minutes. But what exactly causes them has been a mystery for the last 40 years. Now, a team used data from a combination of satellites to identify what is causing these powerful emissions. The answer appears to be charged ions surfing on a kind of wave.
A team of researchers in the UK have observed matter falling into a black hole at 30% the speed of light. This is much faster than anything previously observed. The high velocity is a result of misaligned discs of material rotating around the black hole.
In the 1960s, astronomers began to notice that the Universe appeared to be missing some mass. Between ongoing observations of the cosmos and the the Theory of General Relativity, they determined that a great deal of the mass in the Universe had to be invisible. But even after the inclusion of this “dark matter”, astronomers could still only account for about two-thirds of all the visible (aka. baryonic) matter.
This gave rise to what astrophysicists dubbed the “missing baryon problem”. But at long last, scientists have found what may very well be the last missing normal matter in the Universe. According to a recent study by a team of international scientists, this missing matter consists of filaments of highly-ionized oxygen gas that lies in the space between galaxies.
For the sake of their study, the team consulted data from a series of instruments to examine the space near a quasar called 1ES 1553. Quasars are extremely massive galaxies with Active Galactic Nuclei (AGN) that emit tremendous amounts of energy. This energy is the result of gas and dust being accreted onto supermassive black holes (SMBHs) at the center of their galaxies, which results in the black holes emitting radiation and jets of superheated particles.
In the past, researchers believed that of the normal matter in the Universe, roughly 10% was bound up in galaxies while 60% existed in diffuse clouds of gas that fill the vast spaces between galaxies. However, this still left 30% of normal matter unaccounted for. This study, which was the culmination of a 20-year search, sought to determine if the last baryons could also be found in intergalactic space.
As Michael Shull – a professor of Astrophysical and Planetary Sciences at the University of Colorado Boulder and one of the co-authors on the study – indicated, this wild terrain seemed like the perfect place to look.“This is where nature has become very perverse,” he said. “This intergalactic medium contains filaments of gas at temperatures from a few thousand degrees to a few million degrees.”
To test this theory, the team used data from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope to examine the WHIM near the quasar 1ES 1553. They then used the European Space Agency’s (ESA) X-ray Multi-Mirror Mission (XMM-Newton) to look closer for signs of the baryons, which appeared in the form of highly-ionized jets of oxygen gas heated to temperatures of about 1 million °C (1.8 million °F).
First, the researchers used the COS on the Hubble Space Telescope to get an idea of where they might find the missing baryons in the WHIM. Next, they homed in on those baryons using the XMM-Newton satellite. At the densities they recorded, the team concluded that when extrapolated to the entire Universe, this super-ionized oxygen gas could account for the last 30% of ordinary matter.
As Prof. Shull indicated, these results not only solve the mystery of the missing baryons but could also shed light on how the Universe began. “This is one of the key pillars of testing the Big Bang theory: figuring out the baryon census of hydrogen and helium and everything else in the periodic table,” he said.
Looking ahead, Shull indicated that the researchers hope to confirm their findings by studying more bright quasars. Shull and Danforth will also explore how the oxygen gas got to these regions of intergalactic space, though they suspect that it was blown there over the course of billions of years from galaxies and quasars. In the meantime, however, how the “missing matter” became part of the WHIM remains an open question. As Danforth asked:
“How does it get from the stars and the galaxies all the way out here into intergalactic space?. There’s some sort of ecology going on between the two regions, and the details of that are poorly understood.”
Assuming these results are correct, scientists can now move forward with models of cosmology where all the necessary “normal matter” is accounted for, which will put us a step closer to understanding how the Universe formed and evolved. Now if we could just find that elusive dark matter and dark energy, we’d have a complete picture of the Universe! Ah well, one mystery at a time…
Astronomers have long understood that there is a link between a star’s magnetic activity and the amount of X-rays it emits. When stars are young, they are magnetically active, due to the fact that they undergo rapid rotation. But over time, the stars lose rotational energy and their magnetic fields weaken. Concurrently, their associated X-ray emissions also begin to drop.
Interestingly, this relationship between a star’s magnetic activity and X-ray emissions could be a means for finding potentially-habitable star systems. Hence why an international team led by researchers from Queen’s University Belfast conducted a study where they cataloged the X-ray activity of 24 Sun-like stars. In so doing, they were able to determine just how hospitable these star systems could be to life.
To understand how stellar magnetic activity (and hence, X-ray activity) changes over time, astronomers require accurate age assessments for many different stars. This has been difficult in the past, but thanks to mission like NASA’s Kepler Space Observatory and the ESA’s Convection, Rotation and planetary Transits (CoRoT) mission, new and precise age estimates have become available in recent years.
Using these age estimates, Booth and her colleagues relied on data from the Chandra X-ray observatory and the XMM-Newton obervatory to examine 24 nearby stars. These stars were all similar in mass to our Sun (a main sequence G-type yellow dwarf star) and at least 1 billion years of age. From this, they determined that there was a clear link between the star’s age and their X-ray emissions. As they state in their study:
“We find 14 stars with detectable X-ray luminosities and use these to calibrate the age-activity relationship. We find a relationship between stellar X-ray luminosity, normalized by stellar surface area, and age that is steeper than the relationships found for younger stars…”
In short, of the 24 stars in their sample, the team found that 14 had X-ray emissions that were discernible. From these, they were able to calculate the star’s ages and determine that there was a relationship between their longevity and luminosity. Ultimately, this demonstrated that stars like our Sun are likely to emit less high-energy radiation as they exceed 1 billion years in age.
And while the reason for this is not entirely clear, astronomers are currently exploring various possible causes. One possibility is that for older stars, the reduction in spin rate happens more quickly than it does for younger stars. Another possibility is that the X-ray brightness declines more quickly for older, more slowly-rotating stars than it does for younger, faster ones.
Regardless of the cause, the relationship between a star’s age and its X-ray emissions could provide astronomers and exoplanet hunters with another tool for gauging the possible habitability of a system. Wherever a G-type or K-type star is to be found, knowing the age of the star could help place constraints on the potential habitability of any planets that orbit it.
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.
On a clear night, away from the bright lights of a city, you can see the smudge of the Andromeda galaxy with the naked eye. With a backyard telescope, you can take a good look at the Milky Way’s sister galaxy. With powerful observatories, it’s possible to see deep inside Andromeda, which is what astronomers have been doing for decades.
Now, astronomers combing through data from the ESA’s XMM Newton space telescope have found something rare, at least for Andromeda; a spinning neutron star. Though these objects are common in the Milky Way, (astronomers think there are over 100 million of them) this is the first one discovered in Andromeda.
A neutron star is the remnant of a massive star that went supernova. They are the smallest and most dense stellar objects known. Neutron stars are made entirely of neutrons, and have no electrical charge. They spin rapidly, and can emit electromagnetic energy.
If the neutron star is oriented toward Earth in just the right way, we can detect their emitted energy as pulses. Think of them as lighthouses, with their beam sweeping across Earth. The pulses of energy were first detected in 1967, and given the name pulsar.” We actually discovered pulsars before we knew that neutron stars existed.
Many neutron stars, including this one, exist in binary systems, which makes them easier to detect. They cannibalize their companion star, drawing gas from the companion into their magnetic fields. As they do so, they emit high energy pulses of X-ray energy.
The star in question, which astronomers, with their characteristic flair for language, have named 3XMM J004301.4+413017, spins rapidly: once every 1.2 seconds. It’s neighbouring star orbits it once every 1.3 days. While these facts are known, a more detailed understanding of the star will have to wait for more analysis. But 3XMM J004301.4+413017 does appear to be an exotic object.
“It could be what we call a ‘peculiar low-mass X-ray binary pulsar’ – in which the companion star is less massive than our Sun – or alternatively an intermediate-mass binary system, with a companion of about two solar masses,” says Paolo Esposito of INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan, Italy. “We need to acquire more observations of the pulsar and its companion to help determine which scenario is more likely.”
“We’re in a better position now to uncover more objects like this in Andromeda, both with XMM-Newton and with future missions such as ESA’s next-generation high-energy observatory, Athena,” added Norbert Schartel, ESA’s XMM-Newton project scientist.
This discovery is a result of EXTraS, a European Project that combs through XMM Newton data. “EXTraS discovery of an 1.2-s X-ray pulsar in M31” by P. Esposito et al, is published in the Monthly Notices of the Royal Astronomical Society, Volume 457, pp L5-L9, Issue 1 March 21, 2016.
The combined observations from two generations of X-Ray space telescopes have now revealed a more complete picture of the nature of high-speed winds expelled from super-massive black holes. Scientist analyzing the observations discovered that the winds linked to these black holes can travel in all directions and not just a narrow beam as previously thought. The black holes reside at the center of active galaxies and quasars and are surrounded by accretion discs of matter. Such broad expansive winds have the potential to effect star formation throughout the host galaxy or quasar. The discovery will lead to revisions in the theories and models that more accurately explain the evolution of quasars and galaxies.
The observations were by the XMM-Newton and NuSTAR x-ray space telescopes of the quasar PDS 456. The observations were combined into the graphic, above. PDS 456 is a bright quasar residing in the constellation Serpens Cauda (near Ophiuchus). The data graph shows both a peak and a trough in the otherwise nominal x-ray emission profile as shown by the NuSTAR data (pink). The peak represents X-Ray emissions directed towards us (i.e.our telescopes) while the trough is X-Ray absorption that indicates that the expulsion of winds from the super-massive black hole is in many directions – effectively a spherical shell. The absorption feature caused by iron in the high speed wind is the new discovery.
X-Rays are the signature of the most energetic events in the Cosmos but also are produced from some of the most docile bodies – comets. The leading edge of a comet such as Rosetta’s P67 generates X-Ray emissions from the interaction of energetic solar ions capturing electrons from neutral particles in the comet’s coma (gas cloud). The observations of a super-massive black hole in a quasar billions of light years away involve the generation of x-rays on a far greater scale, by winds that evidently has influence on a galactic scale.
The study of star forming regions and the evolution of galaxies has focused on the effects of shock waves from supernova events that occur throughout the lifetime of a galaxy. Such shock waves trigger the collapse of gas clouds and formation of new stars. This new discovery by the combined efforts of two space telescope teams provides astrophysicists new insight into how star and galaxy formation takes place. Super-massive blackholes, at least early in the formation of a galaxy, can influence star formation everywhere.
Both the ESA built XMM-Newton and the NuSTAR X-Ray space telescope, a SMEX class NASA mission, use grazing incidence optics, not glass (refraction) or mirrors (reflection) as in conventional 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 foot) truss in the case of NuSTAR and over a rigid frame on the XMM-Newton.
The ESA built XMM-Newton was launched in 1999, an older generation design that used a rigid frame and structure. All the fairing volume and lift capability of the Ariane 5 launch vehicle was needed to put the Newton in orbit. The latest X-Ray telescope – NuSTAR – benefits from tens years of technological advances. The detectors are more efficient and faster and the rigid frame was replaced with a compact truss which required all of 30 minutes to deploy. Consequently, NuSTAR was launched on a Pegasus rocket piggybacked on a L-1011, a significantly smaller and less expensive launch system.
So now these observations are effectively delivered to the theorists and modelers. The data is like a new ingredient in the batter from which a galaxy and stars are formed. The models of galaxy and star formation will improve and will more accurately describe how quasars, with their active super-massive black-holes, transition into more quiescent galaxies such as our own Milky Way.
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.