Globular Clusters Archives

September 18, 2024September 20, 2024 by Evan Gough

A Star Was Kicked Out of a Globular Cluster by an Intermediate-Mass Black Hole

The M15 Globular Cluster (aka. Great Hercules Cluster). Astronomers suspect the existence of one or more intermediate-mass black holes at its heart. Credit: NASA/ESA/HST

Astronomers have solid evidence for the existence of stellar-mass black holes and supermassive black holes. However, evidence for Intermediate Black Holes (IMBHs) is more elusive. Their existence remains hypothetical.

However, study by study, evidence is accumulating for IMBHs. The latest comes from the globular cluster M15, where a fast-moving star suggests the presence of something massive. Could it be an elusive IMBH?

June 27, 2024June 27, 2024 by Evan Gough

Webb Sees Globular Clusters Forming in the Early Universe

The Cosmic Gems arc as observed by the JWST. The clusters have the attributes of gravitationally-bound proto-Globular Clusters. Credit: ESA/Webb, NASA & CSA, L. Bradley (STScI), A. Adamo (Stockholm University) and the Cosmic Spring collaboration.

Picture the Universe’s ancient beginnings. In the vast darkness, light was emitted from a particular galaxy only 460 million years after the Big Bang. On the way, the light was shifted into the infrared and magnified by a massive gravitational lens before finally reaching the James Webb Space Telescope.

The galaxy is called the Cosmic Gems arc, and it held some surprises for astronomers.

January 4, 2024January 4, 2024 by Evan Gough

This Globular Cluster is Plunging Toward the Milky Way’s Centre

The galactic cenre is dominated by powerful tidal forces. What happens to globular clusters that get too close? Image Credit: Spitzer Space Telescope/NASA/JPL-Caltech

Globular clusters (GCs) are spherical groups of stars held together by mutual gravity. Large ones can have millions of stars, and the stars tend to be older and have lower metallicity. The Milky Way contains more than 200 globulars, possibly many more, and most of them are in the galaxy’s halo, the outer reaches of the galaxy.

But they’re not all in the halo, and astronomers are keen to find ones nearest the galactic centre. Now, researchers have found one GC that’s plunging toward the Milky Way’s Centre.

October 13, 2023October 13, 2023 by Jon Voisey

The Milky Way’s Stolen Globular Clusters

Modern astronomy holds that all major galaxies (with the Milky Way as no exception) are the accumulation of numerous small mergers. Thus, it should be expected that some of the globular clusters that are now part of our galaxy are likely inherited from other galaxies which have been cannibalized by the Milky Way, or even stolen from intact companion galaxies such as the Magellanic Clouds.

Associations between these clusters and the various progenitors began in the 1990’s, but recent research is beginning to paint a more comprehensive picture on exactly what percentage of our globular clusters were stolen, and precisely which ones.

September 12, 2023September 12, 2023 by Evan Gough

The Hubble Imaged Some Globular Clusters in an Unusual Place: Near the Milky Way’s Centre

Most globular clusters are found in the Milky Way's halo. But some, like the glittering globular cluster Terzan 12, are near the galactic centre. Image Credit: ESA/Hubble & NASA, R. Cohen (Rutgers University)

Our galaxy has about 200 Globular Clusters (GCs,) and most of them are in the galaxy’s halo. Astronomers think most GCs were taken from dwarf galaxies and merged with the Milky Way due to the galaxy’s powerful gravity. That explains why so many of them are on the outskirts of the galaxy. But they’re not all in the halo. Some are towards the Milky Way’s galactic bulge. What are globular clusters doing there?

May 23, 2023May 23, 2023 by Evan Gough

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?

May 16, 2023May 16, 2023 by Brian Koberlein

New Clues to the Formation of Globular Clusters: Their Ultramassive Stars

The scattered stars of the globular cluster NGC 6355 are strewn across this image from the NASA/ESA Hubble Space Telescope. This globular cluster lies less than 50,000 light-years from Earth in the Ophiuchus constellation. Image Credit: ESA/Hubble & NASA, E. Noyola, R. Cohen

Globular clusters are odd beasts. They aren’t galaxies, but like galaxies, they are a gravitationally bound collection of stars. They can contain millions of stars densely packed together, and they are old. Really old. They likely formed when the universe was only about 400 million years old. But the details of their origins are still unclear.

February 13, 2023February 13, 2023 by Evan Gough

Globular Star Clusters are Constantly Kicking Stars out of the Galaxy

Omega Centauri is the brightest globular cluster in the night sky. It holds about 10 million stars and is the most massive globular cluster in the Milky Way. It's possible that globulars and nuclear star clusters are related in some way as a galaxy evolves. Image Credit: ESO.

All the stars we can see with the naked eye are part of the Milky Way. The gravitational power of the galaxy’s combined mass binds the stars to the galaxy. But sometimes stars are evicted from the galaxy.

These stars are called hypervelocity stars, and some of them are born from powerful gravitational interactions in globular clusters.