A Few Tidbits About Supermassive Black Holes

by | May 18, 2018


This artist’s impression shows the dust torus around a super-massive black hole.

Black holes form when a massive star (more than 20x size of the Sun) has used up  it’s fuel, is at the end of its life and collapses in upon itself. This collapse also causes the star to explode, a so-called supernova. The gravity due to the extreme mass and density is so great that the escape velocity (the speed at which something needs to travel to escape the gravity of an object) is greater than the speed of light. Related IFOD on black holes and “Hawking Radiation”: Why Was Stephen Hawking Famous?

At the center of our galaxy – the Milky Way – there is a “supermassive black hole” called Sagittarius A* (pronounced as “Sagattarius A Star”). Sgr A* is thought to be about 4.3 million solar masses (meaning that it has as much mass as 4.3 million Suns) and has a radius of about 1 AU (AU = Astronomical Unit, which is the distance between the Earth and Sun, which is 93 million miles). A black hole that big would likely have formed not from one supernova explosion of a star but rather from multiple massive objects.

This summer a star called SO-2 will pass on it’s orbit within 17 light years of Sgr A* and will provide a fantastic opportunity to learn more about Sgr A* and will provide another test of the theory of general relativity.  Below is a simulation from UCLA of the objects orbiting Sgr A*. In the video young stars are shown in teal green, old stars are shown in orange, and those with unknown spectral type are shown in magenta. The movie begins at the very center of the Galaxy, ~0.015 pc from the supermassive black hole, in the year 1893, and pulls away to a distance of 0.2 pc as the movie reaches the year 2013, ending from the viewing angle of Earth.

Here’s a link to the video in case it doesn’t work in your browser:http://www.astro.ucla.edu/~ghezgroup/gc/videos/ghezGC_comp3-18_H264_864_VP8.webm

It is thought that all major galaxies have supermassive black holes at their center. Some are very active as they eat matter and fire off energy across the electromagnetic spectrum, but others are like Sagittarius A* and are relatively.

A new discovery published last week concerns a truly monstrous black hole that has a mass equal to 20 Billion Suns and it thought to be growing at a rate of about 1% every 1 million years.  That may not sound impressive, but that means that this black hole is eating mass equal to our Sun every two days!!! This black hole is about 12 billion light years away.

“This black hole is growing so rapidly that it’s shining thousands of times more brightly than an entire galaxy, due to all of the gases it sucks in daily that cause lots of friction and heat,” lead study author Christian Wolf, an astronomer at the Australian National University said. “If we had this monster sitting at the center of our Milky Way galaxy, it would appear 10 times brighter than a full moon – it would appear as an incredibly bright pin-point star that would almost wash out all of the stars in the sky.”

Wow.  The universe is a crazy place.

A fun and related IFOD about density: Density!

1 Comment

  1. For a moment I thought this article was going to attempt to dispel the notion of black ice…


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