In the constellation Ursa Major
210 million times the mass of the Sun
Diameter the size of the outer edge of the asteroid belt
Early black hole studies revealed a possible relationship between the mass of a supermassive black hole in the center of a galaxy and the mass of the "bulge" of stars around it. Later studies showed an even tighter relationship between the black hole and the range of orbital speeds for stars within the bulge. These relationships are crucial for understanding the link between the formation of central black holes and their surrounding galaxies.
To better understand this link, astronomers are using Hubble Space Telescope and ground-based telescopes to measure the masses of central black holes and the velocities of the stars around them in many more galaxies.
A study released in 2009, for example, targeted five galaxies, including NGC 4026, a large lens-shaped galaxy that is close by on the galactic distance scale, at just 50 million light-years. The galaxy, which is just to the lower left of the "bowl" of the Big Dipper, is turned almost edge-on as seen from Earth.
The study team included Karl Gebhardt, one of the astronomers who discovered the relationship between the mass of a central black hole and the mass of the surrounding stellar bulge.
The astronomers used two Hubble instruments, the Wide Field Planetary Camera 2 (WFPC2), which takes sharp images of the galaxies, particularly their central regions; and the Space Telescope Imaging Spectrograph, which takes spectra at several locations across a galaxy.
The spectra reveal the orbital speeds of stars at different regions within the galaxy. Stars that are near a supermassive black hole move much more quickly. By measuring the speeds of stars close to the galactic center, astronomers can determine the black hole's mass. Measuring speeds across a larger section of the galaxy reveals how the orbital speed changes at different distances from the black hole.
The astronomers say the observations demonstrate there is a 99.9 percent certainty of a supermassive black hole at the heart of NGC 4026. It is likely between 170 million and 280 million times the mass of the Sun, with the most likely weight at 210 million times the Sun's mass. That places the black hole near the middle of the "supermassive" scale.
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This document was last modified: March 14, 2012.