Astronomers have been puzzling over a mystery for a few years now, and they think they might have an answer. Everywhere you look, there’s a diffuse glow of background X-ray radiation – but where’s it coming from? Astronomers pointed the Chandra X-Ray Observatory at a patch of sky for a total of 23 days over a 2-year period, and resolved 600 separate point sources. This isn’t a background glow at all, but the X-ray radiation from hundreds of millions of supermassive black holes, like the one at the heart of the Milky Way.
An international team of astronomers have analyzed a recent short gamma-ray burst, and they think it’s the last scream of a neutron star being gobbled up by a black hole. The burst was discovered on July 24, 2005 by NASA’s Swift satellite, and then astronomers performed followup observations with a variety of instruments. The length of the explosion and the wavelengths of radiation emitted have led astronomers to the conclusion that it had to be a neutron star colliding with a black hole.
Astronomers were expecting that a massive star in the Westerlund 1 star cluster should have collapsed into a black hole. Instead, it became a neutron star. Since this star was 40 times the mass of the Sun before it collapsed, it should have been a prime black hole candidate. So why did it end up as a neutron star? It’s possible that the star blew off most of its mass at the end of its life, so there just wasn’t enough material to form a black hole.
The Hubble Space Telescope has discovered a supermassive black hole without a surrounding galaxy. These black holes and their galaxies are usually linked, so it’s an unusual discovery. One possibility is that the host galaxy was stripped away during a collision with another galaxy. Another possibility is that the black hole is surrounded by a large amount of material, it’s just dark matter, so Hubble couldn’t detect it.
Monday’s gamma ray burst might have been just what astronomers have been hoping to see for decades – the birth of a new black hole. GRB 050509B was a short gamma ray burst, lasting only 50 milliseconds, which means it could be the result of a collision between two neutron stars, or even two black holes. NASA’s Swift observatory detected the explosion, tracked its location, and focused its large telescope within a minute of its occurrence.
Here’s a relief. Instead of being painfully stretched (aka spaghettified) by the immense tidal forces around a black hole, you’d probably just be roasted by the intense heat. Professor Andrew Hamilton at the University of Colorado predicts that only the smallest black holes would actually stretch you out like this. All the larger, supermassive black holes are already choking on enough material, that their surrounding environment is a superhot plasma heated to millions of degrees and blasting out intense radiation.
Just before matter is gobbled up by a hungry black hole, it’s hurtling around the monster at nearly the speed of light. This heats up the material and it can release a tremendous amount of energy as X-rays. Different elements release energy with a specific fingerprint that astronomers can detect. Researchers from Europe have measured iron as it hurtles around black holes and found a relativistic effect because it’s moving so quickly. The team averaged out the X-ray light from 100 distant black holes to show the telltale signature of material about to be consumed by a black hole.
Researchers have used the Chandra X-Ray Observatory to understand just how large supermassive black holes can get by performing a very detailed census of the mysterious objects. These are the gigantic black holes, with millions of times the mass of our Sun, that sit at the centre of almost every galaxy. The largest of them reach 100 million solar masses and gained this weight early – then they ran out of material to consume. The smaller holes, between 10 and 100 million solar masses, have been more frugal with the gas and dust they consume, and continue to grow to this day.
NASA’s Swift space observatory has seen its first Gamma-Ray Burst (GRB), probably the birth of a black hole. Swift detected the explosion on January 17, and turned to face it within 200 seconds – enough time to watch the explosion with its X-Ray telescope. This is the first time an X-Ray observatory has ever watched a GRB while it was bursting, and not just the afterglow. Swift is still in its checkout phase, so its Ultraviolet/Optical telescope wasn’t ready to image the GRB yet, but it should be ready by February 1.
Astronomers now believe that all large galaxies have a supermassive black hole at their centre, but it was believed that these black holes formed after the galaxy. The evidence is starting to point the other way, that these black holes formed soon after the Big Bang, and then the galaxies built up around them. New observations from the Chandra X-Ray Observatory show a distant quasar that formed less than a billion years after the Big Bang, and was already producing the same amount of energy as twenty trillion Suns.