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Black Holes Encyclopedia


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Alternate Names

NGC 4258




in the constellation Canes Venatici

Finder Chart


24 million light-years


24 million to 38 million times the mass of the Sun


Greater than the distance from Earth to the Sun

Discovery Methods



In the early 1940s, astronomer Carl Seyfert discovered that some spiral galaxies are different from the others. Their cores are much brighter, and they are populated by hot, glowing clouds of hydrogen, helium, and other elements. A great power source inhabited the cores of these galaxies, but with the technology of the day, Seyfert and other astronomers couldn't determine what it was.

Today, astronomers know that the power source is a disk of hot gas around a supermassive black hole. And one of the nearest of these "Seyfert galaxies" is M106, at a distance of just 24 million light-years.

Astronomers have used radio telescopes to draw a detailed map of the galaxy's accretion disk. Water molecules at the edge of the disk are pumped up by the disk's energy, creating bright spots known as masers. The masers trace the disk's size (about two light-years in diameter) and its motion around the central black hole (speeds of about one million miles per hour at the outer edge of the disk). The masers also show that the disk is warped like the brim of a hat, which one side turned up a little, and the other turned down.

From the masers and the motions of stars near the core, astronomers have measured the mass of the black hole at roughly 24 million to 38 million times the mass of the Sun.

Magnetic fields generated by the rapidly spinning disk accelerate some of its hot gas to almost the speed of light and shoot it back into space in the form of two jets, which produce radio waves and other forms of energy. The disks shoot out into space from the black hole's poles, so they are perpendicular to the plane of the disk.



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This document was last modified: January 10, 2011.


Artist's Rendering

Ground-Based Photo

Ground-Based Photo

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