Credit: X-ray: NASA/CXC/Inst. of Astronomy, Taiwan/Y-C Chang; Optical/UV: NASA/ESA/STScI/HST; Image Processing: NASA/STScI/J. DePasquale
Building a Bigger Black Hole
A black hole is a massive object smaller than a certain critical size. When an object of a given mass is squeezed beyond this certain point, its gravitational pull causes the object to essentially collapse forever, eventually forming a region of infinite density called a singularity (we think). For example, you could form a black hole from the Sun if you could compress the Sun from its present size (about 700,000 kilometers in radius) down to a sphere of only 3 kilometers radius. In principle, a black hole can have any mass, as long as it's smaller than this critical size. In reality, black holes masses seem to fall into two main categories: some have masses similar to stars (the so-called stellar mass black holes), and the supermassive black holes found at the centers of (perhaps all) galaxies, and which have masses of millions or even billions of Suns. But is there a connection between the two? Could stellar mass black holes swallow enough matter to grow into supermassive black holes? Astronomers have hotly debated the possible existence of "intermediate mass" black holes (IMBHs for short) - black holes with masses of a few hundred to a few thousand solar masses, which could be the "missing link" between the stellar-mass and supermassive varieties. These IMBHs seem hard to detect by the usual methods (the generation of high energy X-rays, or gravitational waves produced by black hole mergers). Sometimes they can signal their presence by swallowing a star that wanders too close, which can produce transient, tell-tale high-energy X-ray emission as the star is slowly pulled apart by the black hole over the course of weeks or even years. The image above shows a Hubble Space Telescope image of a region of space containing two fuzzy elliptical galaxies. Observation of this field by the Chandra X-ray Observatory in 2009 revealed the sudden presence of an strong X-ray source (shown in purple in the image above) associated with the galaxy in the lower left of the image. Astronomers think that this transient source, called NGC 6099 HLX-1, was created by the tidal disruption of a star, pulled apart by a black hole in the outskirts of the galaxy. Analysis of the X-ray emission from the source showed that the power output in X-rays alone is about 250 million times the power output of the Sun over all energies. This extreme luminosity, the location of the source far from the center of the galaxy, and the temperature of the gas giving rise to the X-ray emission, all suggest that this star was swallowed by an IMBH.
Published: August 4, 2025
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Page Author: Dr. Michael F. Corcoran
Last modified Monday, 11-Aug-2025 22:20:08 EDT