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.
To Your Scattered Photons Go
Yesterday I wrote about the cosmic x-ray background, and I noted that x-ray astronomy, particularly with high-energy x-rays is difficult. But what is it about x-rays that makes x-ray astronomy so challenging?
Background Check
You are likely familiar with the cosmic microwave background, but there is another background that exists, known as the cosmic x-ray background. Just as the cosmic microwave background is a diffuse microwave glow, the cosmic x-ray background is a diffuse x-ray glow. You can see an image of this x-ray background in the image above. It is a false-color image, where red, green and blue represent low, medium and high x-ray energies.
Bubble Pop
Between the vast expanse of stars in our galaxy there is diffuse gas, dust and plasma known as the interstellar medium. It has been known for quite some time through its effects on radio waves and other light sources. But making a detailed map of this medium has been difficult.
Blurred Lines
One of the challenges with observing black holes is that they don’t emit light. Except for the theoretical Hawking radiation, black holes don’t radiate any light because they are simply and extreme warping of space and time. That doesn’t mean we can’t see black holes. Usually there is a great deal of material in the region around a black hole, so we can observe the light coming from this material. For example, we can observe x-rays, radio waves and visible light emitted by the heated plasma in the accretion disk. We can also see jets of material streaming away from the black hole. This tells us a great deal about black holes, but it doesn’t tell us about the specific structure of warped space and time. For that we still need to rely a lot on relativity theory.
Line of Perseus
The Perseus cluster is a massive galactic cluster consisting of thousands of galaxies. It is often a focus of study because it is both massive and reasonably close (about 240 million light years away). Recently we’ve discovered some interesting x-rays coming from the region. The results have been published the Astrophysical Journal, showing there is an unexplained emission line in the x-ray spectrum.
Survey Says
The image below is the first complete x-ray survey of the Andromeda galaxy. The Andromeda galaxy (also known as M31) is about 2.5 million light years away. It is a spiral galaxy very similar to our own Milky way, so surveys of Andromeda are very useful in understanding galaxies like ours.
Ingredient X
X-ray astronomy presents an additional challenge because you not only have to put your x-ray telescope in space, you also have to build your telescope very differently.
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