An ultraluminous x-ray source (ULX) is an intense, localized sources of x-rays. They are generally powered by solar-mass black holes, similar to the way quasars and blazars are powered by supermassive black holes. We’ve generally thought only black holes could provide enough power to generate such powerful x-rays, but now it seems that isn’t always the case. New results have been published in Nature that show some of them might be powered by accreting neutron stars.
Echoes of Light
The supermassive black hole in the center of our galaxy, known as Sagittarius A*, is pretty quiet for a black hole. It does however flare up from time to time, when material is captured, as can be seen in images from the NuSTAR x-ray telescope. Of course, x-ray astronomy with enough sensitivity to observe x-ray flares at galactic center is …
The Gravity Tango
The image above shows two supermassive black holes orbiting each other. It is a composite image where the blue/white indicates x-rays and the pink indicates radio wavelengths. It may look like they are orbiting closely, but the black holes are about 25,000 light years apart, which is about the same distance the Sun is from the center of the Milky Way.
Yes, Virginia, There Are Black Holes
Recent headlines have proclaimed “Black Holes Don’t Exist!” They’re wrong. Black holes absolutely exist. We know this observationally. We know by the orbits of stars in the center of our galaxy that there is a supermassive black hole in its center. We know of binary black hole systems. We’ve found the infrared signatures of more than a million black holes. …
Big Bang Burger Bar
Lately there’s been news of a radical new theory proposing that the universe began from a hyper-dimensional black hole. Most of the reports seem to stem from an article posted a while back on the Nature blog, which references the original paper. So let’s have a little reality check.
A Million Star Sky
On a dark night with good viewing conditions, you might be able to see about 4,000 stars with the naked eye. Imagine, then, if you could see a million stars with the naked eye. For such a sky, our galaxy would need to be much more densely packed. While we won’t see such a sky anytime soon, it could exist on a planet in the most densely packed galaxy yet discovered. It is known as M60-UCD1, and it is a rather curious galaxy.
Hole-y War
Yesterday I talked about black hole thermodynamics, specifically how you can write the laws of thermodynamics as laws about black holes. Central to the idea of thermodynamics is the property of entropy, which can be related to the amount of physical information a system has.
Black Hole Thermodynamics
In the 1800s scientists studying things like heat and the behavior of low density gases developed a theory known as thermodynamics. As the name suggests, this theory describes the dynamic behavior of heat (or more generally energy). The core of thermodynamics is embodied by its four basic laws.
Fuzzy Wuzzy
According to general relativity, a black hole has three measurable properties: mass, rotation (angular momentum), and charge. That’s it. If you know those three things, you know all there is to know about the black hole. If the black hole is interacting with other objects, then the interactions can be much more complicated, but an isolated black hole is just mass, rotation and charge.