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Monster Galaxy Tosses Stars to the Cosmic Curb

This artist's illustration shows the hypervelocity star cluster HVGC-1 escaping from the supergiant elliptical galaxy M87. HVGC-1 is the first runaway star cluster discovered by astronomers. It is fated to drift through intergalactic space. David A. Aguilar (CfA)
This artist’s illustration shows the hypervelocity star cluster HVGC-1 escaping from the supergiant elliptical galaxy M87. HVGC-1 is the first runaway star cluster discovered by astronomers. It is fated to drift through intergalactic space. Credit: David A. Aguilar (CfA)

Talk about getting the cosmic boot! One of the largest known galaxies in the universe, Messier 87 (M87), appears to have hurled an entire star cluster in our direction. 

No need to worry: Even though the star cluster is clocked at moving near two million miles (3.2 million kilometers) per hour, all the action is happening some 55 million light-years from Earth.

Astronomers are left scratching their heads, however, since they have never before seen an entire cluster containing thousands of stars ejected from its host galaxy.

“Astronomers have found runaway stars before, but this is the first time we’ve found a runaway star cluster,” says lead author of the new study, Nelson Caldwell, an astronomer at the Harvard-Smithsonian Center for Astrophysics.

Dubbed HVGC-1, the ejected globular cluster is a giant ball of stars a few dozen light-years wide. The researchers theorize that it may have wandered a bit too close to one of the supermassive black holes at the center of the M87 galaxy. The black hole perhaps acted as a gravitational slingshot, hurling the hapless cluster at high speed out into deep space.

Globular clusters such as HVGC-1 are considered cosmic fossils because they contain some of the oldest known stars in the universe. They are frequent companions to most galaxies, including our own. At least 150 globular clusters circle the periphery of the Milky Way like a halo.

A Hubble Space Telescope image shows a jet of superhot gas racing away from the nucleus of M87 at 99 percent of the speed of light. The jet spans several thousand light-years. Credit: NASA, Hubble Heritage Team (STScI/AURA)
A Hubble Space Telescope image shows a jet of superhot gas racing away from the nucleus of M87 at 99 percent of the speed of light. The jet spans several thousand light-years. Credit: NASA, Hubble Heritage Team (STScI/AURA)

As for the galactic bully M87, its claim to fame is that it is one of the strongest x-ray emitters in the universe. The galaxy contains not one, but two monster black holes at its heart, the result of an ancient collision and merger with another galaxy. A distinctive, eruptive jet emanates from M87′s nucleus, fed by vast amounts of matter falling into the supermassive black holes.

And what of the fate of the banished cluster? Astronomers say it is destined for a lonely future wandering intergalactic space for the rest of time.

The study will be published in the Astrophysical Journal Letters and is available online.

See for Yourself

Messier 87 is a titan when it comes to galaxies, burning bright with the power of six trillion suns. As a result, it is one of the brightest galaxies in the night sky at magnitude 8.6, and it is an easy target even for small backyard telescopes this time of the year.

This skychart shows the southeast sky after nightfall early May with constellations Virgo and  Leo acting as guideposts in finding the bright galaxy M87 through telescopes. Credit: Starry Night Software- A.Fazekas
This sky chart shows the southeast sky after nightfall in early May, with constellations Virgo and Leo acting as guideposts in finding the bright galaxy M87 through telescopes. Credit: Starry Night Software/A. Fazekas

The giant elliptical galaxy is located in the springtime Virgo, the Maiden, which is now high in the southern evening sky.

Virgo has a reputation as a veritable paradise for galaxy hunters. There are literally scores of galaxies scattered in this part of the sky that are well within the view of most backyard telescopes. M87 is one of the brightest targets, and it is in fact located between an imaginary line connecting two other bright galaxies, M58 and M84. Through a telescope’s eyepiece, this galactic powerhouse looks like a round, grayish glow with a bright center.

Messier 87 galaxy lies buried within the Virgo Cluster of galaxies in the northwester portion of the Virgo constellation.  Credit: Starry Night software - A.Fazekas
Messier 87 galaxy lies buried within the Virgo cluster of galaxies in the northwestern portion of the Virgo constellation. Credit: Starry Night Software/A. Fazekas

The constellation Virgo has a high concentration of galaxies. Astronomers have discovered that they actually belong to the same gigantic group called the Virgo cluster, the center of which lies about 50 million light-years from our own Milky Way galaxy.

Follow Andrew Fazekas, the Night Sky Guy, on TwitterFacebook, and his website.