Tuesday, January 31, 2012

Quasars- A Hot Topic

Okay, terrible pun. We're off to a bad start.
I find celestial objects such as stars, black holes, and quasars to be very fascinating, so I will be doing a series of posts relating to them, one at a time. I find the observation of phenomena to be preferable to long calculations, sot it all works out. Anyway, Quasars.
"What is a quasar?"
Thanks for asking, hypothetical reader. Quasars are extremely bright objects seen in other galaxies, far brighter than anything around them. In fact, the brightest quasars have luminosities exceeding that of entire galaxies. Like most super-hot objects, such as stars and active galaxies, they give off radiation. In particular, quasars give off large amounts of X-rays and radio waves. Like blackbody radiators, older quasars have absorption ranges due to surrounding dust and gas. Newer quasars, however, do not.
"That's what quasars do, I asked what they are."
Sorry, I got a little off track. Long story short, quasars are a side-effect of a black hole. When a black hole pulls in huge amounts of gas and dust, that material can begin orbiting the black hole at extreme speeds, sometimes approaching the speed of light. In the process, this material can give off large amounts of radiation. This is because in the presence of magnetic fields, these fast-moving particles will radiate radio waves in a process called "Synchotron Radiation." These quasi-stellar radio sources, of "quasars," are usually at center of a galaxy, having formed around a super-massive black hole. Super-massive black holes are usually hundreds of thousands or even millions of solar masses in mass.
"What does that look like?"
Here you go.
In this image, you can see the superheated gas spiraling into a black hole, which, obviously, can't be seen, but is at the center. The white line coming from the center at about 100 degrees is called a jet, and, as I intend to talk about them in another post, I won't say anything now.
This particular image illustrates a particularly bright quasar discovered by the European Southern Observatory, or ESO. The mass of this quasar is around two billion solar masses, and is the brightest early-universe object yet discovered.
Quasars are generally so bright that they entirely obscure the galaxy around them. This is rather impressive, given that they are actually much, much smaller than their host galaxy. This is due to a number of factors. First, even the nearest quasars are quite distant, between 600 million and 28 billion lightyears away. This distance makes it difficult to resolve these objects. The other reason is simply because they are so absurdly bright compared to their surroundings. The brightest readily apparent quasar is "3C 273," which is located in the Virgo constellation, as well as having a catchy name. It has an apparent magnitude of 12.8, which is bright enough to be seen through a common telescope. Combining the extreme distance of some quasars with their great brightness makes it quite difficult to resolve the galaxy around them from the quasar itself.
"Where do quasars come from?"
Good question, hypothetical reader. So good, in fact, that nobody knows the answer. You see, existing quasars are very old, as they are only seen in developing galaxies. It is entirely possible that many of the quasars we observe no longer exist, and we're only seeing their light trail.
"No longer exist? Where do they go?"
Well, since quasars are gas and dust spiraling into black holes, eventually they simply run out of material. When this happens, there isn't any dust left to radiate, so the quasar goes quiet, and all that is left is a super-massive black hole. Quasars are certainly capable of taking a lot of material with them. The brightest ones can consume 1000 solar masses annually, and the largest can consume 600 earth masses per minute. I'm just glad we're not near one.
All in all, quasars are interesting structures, very different from the stars and planets we're used to observing. Being so old, they give a glimpse into the early universe. Perhaps I'll do a follow-up post describing exactly what they tell us about way-back-when sometime.
Until then, thanks for ready, and later.

No comments:

Post a Comment