Where Are the Missing Black Holes? The Hubble May Have Helped Find One

This Hubble Space Telescope image shows the globular cluster Messier 4. It contains several hundre thousand stars, and its center might host an elusive intermediate-mass black hole. The black hole could have 800 solar masses. Image Credit: ESA/Hubble & NASA

Most black holes are stellar mass black holes. They’re created when a star several times more massive than our Sun reaches the end and collapses in on itself. There are also supermassive black holes (SMBH,) the behemoths at the center of galaxies that can boast billions of times more mass than the Sun.

But where are the intermediate-mass black holes?

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Messier 4 (M4) – The NGC 6121 Globular Cluster

This M4 globular cluster, as imaged by the Wide Field Imager at ESO’s La Silla Observatory. Credit: ESO

During the late 18th century, Charles Messier began to notice that a series of “nebulous” objects in the night sky that he originally mistook for comets. In time, he would notice that they were in fact something significantly different. With the hope of preventing other astronomers from making the same mistake, he began compiling a list of these in what would come to be known as the Messier Catalog.

Consisting of 100 objects, the catalog became an important milestone in both astronomy and the research of Deep Sky objects. Among the many famous objects in this catalog is the M4 loose globular cluster (aka. NGC 6121). Located in the Scorpius (Scorpio) Constellation, this great cluster of ancient stars is one of the closest Messier Objects of its kind to Earth.

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