How To Weigh a Black Hole: Just Look At Its Galaxy

Article written: 2 Jun , 2008
Updated: 24 Dec , 2015
by

My father was a rancher, who had the uncanny ability to accurately estimate the weight of each animal in his herd of cattle simply by looking at them. Today, at the American Astronomical Society meeting in St. Louis, astronomers announced a new, simple way of determining masses of super-massive black holes by just looking at images of galaxies. Dr. Marc Seigar from the University of Arkansas at Little Rock has been studying images available at the Hubble Space Telescope archive site, and looking at the how tightly the galaxy’s arms wrap around itself in relation to the size of the galaxy’s super-massive black hole. “This provides a much simpler method of determining black hole mass,” said Seigar. “You just need an image of a galaxy and you can measure the tightness of the spiral structure. This can easily be applied to distant galaxies, up to 8 billion light-years away.”

Usually astronomers determine masses of super-massive black holes by looking at how fast the stars are moving in the central regions of the galaxies. But that method only works for nearby galaxies. Astronomers have been looking for a new method for galaxies that are father away. This new inexpensive method can use already-existing images, as Seigar has used from the Hubble Site.

Seigar and his team looked at photographs of 27 spiral galaxies including the Milky Way and the Andromeda Galaxy. They observed galaxies with the smallest black holes had spiral arms with angles up to 43 degrees between the arms and the central bulge. Those with the biggest black holes had spiral arms at angles of only 7 degrees between the arms and the bulge.

Seigar said its also possible that the main factor in determining the mass of a super massive black hole is the amount of central concentration of dark matter in a galaxy. “We think dark matter is driving most of the relationships between black holes and their galaxies,” he said. “The masses of these black holes can be determined indirectly from the characteristics of the light emitted from in falling material.”

Seigar will continue to use this method to verify his findings, as well as looking at other aspects. “We have to determine if the relationship between spiral arms and black hole mass evolves over time.”

Source: AAS press conference


7 Responses

  1. LLDIAZ says

    Most of the things we read about are just speculation they are’nt considered fact until tested and proven……

  2. greg is your last name says

    “Seigar will continue to use this method to verify his findings”

    so not quite proven as of yet.

  3. Astrofiend says

    Seems like it would be useful for rough estimates, but not too much more, yet.

    Still, it’s an interesting correlation. There’d be some interesting physics involved in that I reckon.

  4. Sakib says

    That amazing image of the Andromeda Galaxy is by Rob Gendler! It is really saddening that his name his not mentioned, he spent hundreds of hours making that picture and yet he doesn’t get a credit. Bet if it was a Hubble picture it would proudly proclaim it was a Hubble picture.

  5. sethumadhavan says

    Is black hole the end result of transformation of energy from matter?

  6. amit says

    can u tel me when is our galaxy colliding with the andromeda galaxy.i think scientist said that if our earth will definetely fall in the centre of the black hole SAGITTARIUS .or it will be thrown out of our galaxy.can you tel me wot is the aurora formation.and if every galaxy has black hole in its centre like in milky way then why there is not any effect on our solar system

  7. This is NOT my real name says

    I believe one way the world might end is a black hole, but we won’t be around, also I think the Andromeda is going to collide with the Milky Way.

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