The emission nebula N44 in our neighboring galaxy the Large Magellanic Cloud has a large, 250 light-year hole and astronomers are trying to figure out why.
One possibility is particle winds expelled by massive stars in the bubble’s interior that are pushing out the glowing gas. This answer was found to be inconsistent with measured wind velocities. Another possibility is that the expanding shells of old supernovas have sculpted the unusual space cavern. An unexpected clue of hot X-ray emitting gas was recently been detected escaping the N44 superbubble. The featured image was taken in three very specific colors by the huge 8-meter Gemini South Telescope.
This artist’s concept illustrates a supermassive black hole with millions to billions times the mass of our sun. Supermassive black holes are enormously dense objects buried at the hearts of galaxies. (Smaller black holes also exist throughout galaxies.) In this illustration, the supermassive black hole at the center is surrounded by matter flowing onto the black hole in what is termed an accretion disk. This disk forms as the dust and gas in the galaxy falls onto the hole, attracted by its gravity.
Also shown is an outflowing jet of energetic particles, believed to be powered by the black hole’s spin. The regions near black holes contain compact sources of high energy X-ray radiation thought, in some scenarios, to originate from the base of these jets. This high energy X-radiation lights up the disk, which reflects it, making the disk a source of X-rays. The reflected light enables astronomers to see how fast matter is swirling in the inner region of the disk, and ultimately to measure the black hole’s spin rate. Image credit: NASA/JPL-Caltech
Universe’s largest structure caught in the act of forming
“The Universe forms a vast cosmic web where filaments interconnect, with matter flowing along them into a nexus. At the centers of these intersections, the most massive galaxy clusters form. Over time, more clusters fall in, creating the largest structures of all. The Hubble Space Telescope recently observed one of them, MACS J0717, revealing four separate clusters in the collision process.”
When it comes to the largest bound cosmic structures, it doesn’t get any bigger than galaxy clusters. Unless, that it, you consider when multiple galaxy clusters merge together. Located at the intersections of cosmic dark matter filaments, smaller clusters flow into the larger clusters located at such a nexus. When we get very lucky, colliding clusters can be seen. Recently, scientists have located a cosmic smash-up between four such clusters in the large structure MACS J0717.5+3745. One of the clusters within is moving so quickly – 3,000 km/s – that the light within it gets shifted thanks to the speed of the electrons within it. X-ray, radio and optical/IR data combine to reveal a treasure trove of information, including active galaxies, a separation between normal and dark matter and even information about the inflows along the cosmic filaments.
The cosmic swirl of giant waves in an enormous reservoir of glowing hot gas are visible in this enhanced X-ray image from the Chandra Observatory. The frame spans over 1 million light-years across the center of the nearby Perseus Galaxy Cluster. With temperatures in the tens of millions of degrees, the gas glows brightly in X-rays. Computer simulations can reproduce details of the structures sloshing through the Perseus cluster’s X-ray hot gas, including the remarkable concave bay seen below and left of center. About 200,000 light-years across, twice the size of the Milky Way, the bay’s formation indicates that Perseus itself was likely grazed by a smaller galaxy cluster billions of years ago.
NASA, CXC, GSFC, Stephen Walker, et al.
When a massive star exploded in the Large Magellanic Cloud, a satellite galaxy to the Milky Way, it left behind an expanding shell of debris called SNR 0519-69.0. Here, multimillion degree gas is seen in X-rays from Chandra (blue). The outer edge of the explosion (red) and stars in the field of view are seen in visible light from Hubble.
ASTROPHYSICISTS FROM THE LOMONOSOV MOSCOW STATE UNIVERSITY
HAVE STUDIED THE “REJUVENATING” PULSAR IN A NEIGHBORING GALAXY
Lomonosov Moscow State University scientists have published in the Astrophysical Journal the results of a study of the unique ultraslow pulsar XB091D. This neutron star is believed to have captured a companion only a million years ago and, since then, has been slowly restoring its rapid rotation. The young pulsar is located in one of the oldest globular star clusters in the Andromeda galaxy, where the cluster may once have been a dwarf galaxy.
Massive stars die young, exploding as bright supernovae. In this process, their outer layers of material are thrown off, and the core shrinks, usually becoming a compact and super-dense neutron star. Strongly magnetized, they rotate rapidly, making hundreds of revolutions per second, but they lose their rotational energy and slow down, emitting narrow beams of particles. They radiate a focused radio emission that periodically passes the Earth, creating the effect of a regularly pulsating source, often with a millisecond period.
In order to “return youth” and again accelerate its rotation, the pulsar can encounter an ordinary star. After teaming up to form a pair or a binary system, the neutron star begins to pull matter from the star, forming a hot accretion disk around itself. Closer to the neutron star, the gaseous disk is torn apart by the magnetic field of the neutron star, and the matter streams onto it, forming a “hot spot” – the temperature here reaches millions of degrees, and the spot radiates in X-rays. A rotating neutron star can then be seen as an X-ray pulsar as a beacon, while the matter that continues to fall on it gives an additional impulse, accelerating the rotation.
For some hundred thousand years – a mere blink in the history of the universe – the old pulsar, which has already slowed to one revolution every few seconds, can once again spin thousands of times faster. Such a rare moment was observed by a team of astrophysicists from the Lomonosov Moscow State University, jointly with colleagues from Italy and France. The X-ray pulsar known as XB091D, was discovered at the earliest stages of its “rejuvenation” and turns out to be the slowest rotating of all globular-cluster pulsars known to date. The neutron star completes one revolution in 1.2 seconds – more than ten times slower than the previous record holder. According to scientists, the acceleration of the pulsar began less than one million years ago.
The discovery was made using observations collected by the XMM-Newton space observatory between 2000 and 2013 and were combined by astronomers of the Lomonosov Moscow State University into an open online database. Access to information on approximately 50 billion X-ray photons has already allowed scientists from different countries to discover a number of previously unnoticed interesting objects. Among them was the pulsar XB091D, which was also noticed by another group of Italian astronomers who published their results several months ago. XB091D is only the second pulsar found outside of our galaxy and its nearest satellites, although two more such pulsars were subsequently detected using the same online catalog.
The results of the first complete analysis of the X-ray source XB091D are presented in an article published by Ivan Zolotukhin, a researcher at the Lomonosov Moscow State University, and his co-authors in The Astrophysical Journal.
“The detectors on XMM-Newton detect only one photon from this pulsar every five seconds. Therefore, the search for pulsars among the extensive XMM-Newton data can be compared to the search for a needle in a haystack, “ says Ivan Zolotukhin. – In fact, for this discovery we had to create completely new mathematical tools that allowed us to search and extract the periodic signal. Theoretically, there are many applications for this method, including those outside astronomy. “
Based on a total of 38 XMM-Newton observations, astronomers managed to characterize the XB091D system. The X-ray pulsar is about 1 million years old, the companion of the neutron star is an old star of moderate size (about four fifths the mass of the Sun). The binary system itself has a rotation period of 30.5 hours, and the neutron star spins once on its axis every 1.2 seconds. In about 50 thousand years, it will accelerate sufficiently to turn into a conventional millisecond pulsar.
However, it was not only orbital parameters that astronomers were able to observe, they were also able to determine the environment around XB091D. Ivan Zolotukhin and his colleagues showed that XB091D is located in the neighboring Andromeda galaxy, 2.5 million light-years away, amongst the stars of the extremely dense globular cluster B091D, where in a volume of only 90 light-years across, there are more millions of old faint stars. The cluster itself is estimated to be as much as 12 billion years old, so no recent supernovae resulting in the birth of a pulsar would have occurred.
“In our galaxy, no such slow X-ray pulsars are observed in hundred and fifty known globular clusters, because their cores are not big and dense enough to form close binary stars at sufficiently high rate” explains Ivan Zolotukhin. – This indicates that the B091D cluster core, with an extremely dense composition of stars in the XB091D is much larger than that of the usual cluster. So, we are dealing with a large and rather rare object – with a dense remnant of a small galaxy that the Andromeda galaxy once devoured. The density of the stars here, in a region that is about 2.5 light-years across, is about ten million times higher than in the vicinity of the Sun.”
According to scientists, it is the vast region of super-high density stars in the B091D cluster that allowed a neutron star to capture a companion about a million years ago and begin the process of acceleration and “rejuvenation.”
Messier 74 ( NGC 628) is a Grand Design spiral galaxy located at 32 million light-years from Earth, 1.5° east-northeast of Eta Piscium, the brightest star in the constellation Pisces. It is the brightest member of the M74 Group, a group of 5-7 galaxies.
The Chandra X-ray Observatory had observed an ultraluminous X-ray source (ULX) in M74, radiating more X-ray power than a neutron star in periodic intervals of around two hours. It has an estimated mass of around 10,000 Suns. This is an indicator of an intermediate-mass black hole. This would be a rather uncommon class of black holes, somewhere in between in size of stellar black holes and the massive black holes theorized to reside in the center of many galaxies. Because of this, they are believed to form not from single supernovae, but possibly from a number of lesser stellar black holes in a star cluster.
Two supernovae have been identified in M74, SN 2002ap, a Type Ic (or hypernova) and SN 2003gd, a Type II-P supernova.
Centaurus A is the fifth brightest galaxy in the sky – making it an ideal target for amateur astronomers – and is famous for the dust lane across its middle and a giant jet blasting away from the supermassive
black hole at its center. Cen A is an active galaxy about 12 million
light years from Earth.
Cosmic Cluster Collision Triggers Trio Of Active Galaxies
“When the clusters collide, their mutual gravity causes an incredibly energetic cosmic smash-up, heating the gas to such high temperatures they emit X-rays. Mysteriously, on the outskirts of the collision, intense radio emission can be found. The fact that these two signals are offset indicate that there’s another, secondary process at work.”
When two galaxy clusters collide, there are a slew of cosmic certainties you can bet on: all the galaxies will miss one another, the intracluster gases will collide and heat up, and X-rays will be emitted. But on rare occasion, radio emission can be found, too. Which is a puzzle, since that requires electrons to gain an extra factor of 1,000,000 in energy! How can that happen? Up until recently, it was a mystery, but a new colliding cluster, Abell 3411 and 3412, has shown something incredible: gas shocks on the outskirts of the X-ray collisions appear to get a blast from nearby, active supermassive black holes, giving the electrons the needed boost and creating those energetic electrons after all!
Most galaxies have a spiral or elliptical structure. About a
quarter of galaxies, though, look quite messy. Known as irregular galaxies, this group includes NGC 5408 above.
John Herschel recorded the existence of NGC 5408 in 1834. Astronomers had long mistaken it for a planetary nebula, an expelled cloud of material from an aging star. Instead, it turned out to be an entire galaxy, located about 16 million light-years from Earth in the constellation of Centaurus (The Centaur).
In yet another sign of NGC 5408 breaking convention, the galaxy is associated with an object known as an ultraluminous X-ray source, one of the best studied of its class. These rare objects beam out
huge amounts of
energetic X-rays. Astrophysicists believe these sources to be strong candidates for intermediate-mass black holes. This hypothetical type of black hole has a good deal more mass than the black holes formed when giant stars collapse. (x)
When a star runs out of nuclear fuel, it will collapse. If the core, or central region, of the star has a mass that is greater than three Suns, no known nuclear forces can prevent the core from forming a deep gravitational warp in space called a black hole.
A black hole does not have a surface in the usual sense of the word. There is simply a region, or boundary, in space around a black hole beyond which we cannot see.
This boundary is called the event horizon. Anything that passes beyond the event horizon is doomed to be crushed as it descends ever deeper into the gravitational well of the black hole. No visible light, nor X-rays, nor any other form of electromagnetic radiation, nor any particle, no matter how energetic, can escape. The radius of the event horizon (proportional to the mass) is very small, only 30 kilometers for a non-spinning black hole with the mass of 10 Suns.
Can astronomers see a black hole? Not directly. The only way to find one is to use circumstantial evidence. Observations must imply that a sufficiently large amount of matter is compressed into a sufficiently small region of space so that no other explanation is possible. For stellar black holes, this means observing the orbital acceleration of a star as it orbits its unseen companion in a double or binary star system.
Searching for black holes is tricky business. One way to locate them has been to study X-ray binary systems. These systems consist of a visible star in close orbit around an invisible companion star which may be a neutron star or black hole. The companion star pulls gas away from the visible star.
As this gas forms a flattened disk, it swirls toward the companion. Friction caused by collisions between the particles in the gas heats them to extreme temperatures and they produce X-rays that flicker or vary in intensity within a second.
Many bright X-ray binary sources have been discovered in our galaxy and nearby galaxies. In about ten of these systems, the rapid orbital velocity of the visible star indicates that the unseen companion is a black hole. The X-rays in these objects are produced by particles very close to the event horizon. In less than a second after they give off their X-rays, they disappear beyond the event horizon.
However, not all the matter in the disk around a black hole is doomed to fall into the black hole. In many black hole systems, some of the gas escapes as a hot wind that is blown away from the disk at high speeds. Even more dramatic are the high-energy jets that radio and X-ray observations show exploding away from some stellar black holes. These jets can move at nearly the speed of light in tight beams and travel several light years before slowing down and fading away.
Do black holes grow when matter falls into them? Yes, the mass of the black hole increases by an amount equal to the amount of mass it captures. The radius of the event horizon also increases by about 3 kilometers for every solar mass that it swallows. A black hole in the center of a galaxy, where stars are densely packed, may grow to the mass of a billion Suns and become what is known as a supermassive black hole.
The Milky Way’s close neighbor, Andromeda, features a dominant source of high-energy X-ray emission, but its identity was mysterious until now. As reported in a new study, NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array) mission has pinpointed an object responsible for this high-energy radiation.
The object, called Swift J0042.6+4112, is a possible pulsar, the dense remnant of a dead star that is highly magnetized and spinning, researchers say. This interpretation is based on its emission in high-energy X-rays, which NuSTAR is uniquely capable of measuring. The object’s spectrum is very similar to known pulsars in the Milky Way.
It is likely in a binary system, in which material from a stellar companion gets pulled onto the pulsar, spewing high-energy radiation as the material heats up.
“We didn’t know what it was until we looked at it with NuSTAR,” said Mihoko Yukita, lead author of a study about the object, based at Johns Hopkins University in Baltimore. The study is published in The Astrophysical Journal.
This candidate pulsar is shown as a blue dot in a NuSTAR X-ray image of Andromeda (also called M31), where the color blue is chosen to represent the highest-energy X-rays. It appears brighter in high-energy X-rays than anything else in the galaxy.
The study brings together many different observations of the object from various spacecraft. In 2013, NASA’s Swift satellite reported it as a high-energy source, but its classification was unknown, as there are many objects emitting low energy X-rays in the region. The lower-energy X-ray emission from the object turns out to be a source first identified in the 1970s by NASA’s Einstein Observatory. Other spacecraft, such as NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton had also detected it. However, it wasn’t until the new study by NuSTAR, aided by supporting Swift satellite data, that researchers realized it was the same object as this likely pulsar that dominates the high energy X-ray light of Andromeda.
Traditionally, astronomers have thought that actively feeding black holes, which are more massive than pulsars, usually dominate the high-energy X-ray light in galaxies. As gas spirals closer and closer to the black hole in a structure called an accretion disk, this material gets heated to extremely high temperatures and gives off high-energy radiation. This pulsar, which has a lower mass than any of Andromeda’s black holes, is brighter at high energies than the galaxy’s entire black hole population.
Even the supermassive black hole in the center of Andromeda does not have significant high-energy X-ray emission associated with it. It is unexpected that a single pulsar would instead be dominating the galaxy in high-energy X-ray light.
“NuSTAR has made us realize the general importance of pulsar systems as X-ray-emitting components of galaxies, and the possibility that the high energy X-ray light of Andromeda is dominated by a single pulsar system only adds to this emerging picture,” said Ann Hornschemeier, co-author of the study and based at NASA’s Goddard Space Flight Center, Greenbelt, Maryland.
Andromeda is a spiral galaxy slightly larger than the Milky Way. It resides 2.5 million light-years from our own galaxy, which is considered very close, given the broader scale of the universe. Stargazers can see Andromeda without a telescope on dark, clear nights.
“Since we can’t get outside our galaxy and study it in an unbiased way, Andromeda is the closest thing we have to looking in a mirror,” Hornschemeier said.
NuSTAR is a Small Explorer mission led by Caltech and managed by JPL for NASA’s Science Mission Directorate in Washington. NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corp., Dulles, Virginia. NuSTAR’s mission operations center is at UC Berkeley, and the official data archive is at NASA’s High Energy Astrophysics Science Archive Research Center. ASI provides the mission’s ground station and a mirror archive. JPL is managed by Caltech for NASA.
Dark Matter Proved Real By Colliding Galaxy Clusters
“If you look at rotating galaxies or the motions of galaxies within clusters, there’s a mismatch between the matter we see and the gravitational effects we observe. Even on the largest scales, the way galaxies clump and cluster together cannot be explained without some new physics. Observations show that it can’t be gas, dust, plasma or black holes; there’s truly something unaccounted for. Attempts to modify gravity can solve some of these problems, but the leading explanation is a new type of matter: dark matter.”
Dark matter is a puzzle that’s now more than 80 years old: the presence of all the known, observable, detectable normal matter — the stuff in the standard model — cannot account for the gravitation of the astronomical objects we observe. But despite our inability to create or detect it in a laboratory, we’re certain of its existence in the Universe. The true test of this comes from colliding galaxy clusters, which show a distinct separation between all the known “normal” components, which collide, heat up and emit light, and the gravitational components, which very clearly don’t. At this point, over a dozen distinct colliding clusters show this effect, from some of the smallest known galactic groups to the largest colliding cluster in the Universe: El Gordo.
Some galaxies have extremely bright cores, suggesting that they contain a supermassive black hole that is pulling in matter at a prodigious rate. Astronomers call these “active galaxies,” and Hercules A is one of them. In visible light, Hercules A looks like a typical elliptical galaxy. In X-ray light, however, Chandra detects a giant cloud of
multimillion-degree gas (purple). This gas has been heated by energy
generated by the infall of matter into a black hole at the center of
Hercules A that is over 1,000 times as massive as the one in the middle
of the Milky Way. Radio data (blue) show jets of particles streaming
away from the black hole. The jets span a length of almost one million
Most Powerful Black Hole Jet Ever Spotted By NASA’s Chandra
“From 500 million light years away, the Chandra X-ray telescope has mapped out a 300,000 light year-long jet coming from the galaxy Pictor A. Like many active galaxies, it’s powered by a supermassive black hole many millions or even billions of times the mass of our Sun.”
When supermassive black holes have a large amount of matter fall onto them, they accelerate a large amount of the ionized material – particularly electrons – into high-velocity, bi-directional jets. In many cases, those jets of material collide with previously blown-off gaseous material and create high-energy X-rays. While these can often be visible across the cosmos, it’s very rare to have a jet so large. The galaxy Pictor A, imaged by Chandra over a 15 year timescale, has the longest known such jet at 300,000 light years, culminating in a “hot spot” shockwave, where the electrons collide with the gas at greater than the speed of sound. A counterjet, invisible with all other telescopes, was also found by Chandra.