Hypervelocity stars Archives

February 6, 2025February 6, 2025 by Evan Gough

There Could Be a Supermassive Black Hole in the Large Magellanic Cloud Hurling Stars at the Milky Way

This beautiful image shows the Large and Small Magellanic Cloud above the ESO's Paranal Observatory and the four Auxiliary Telescopes of the Very Large Telescope (VLT) Array. New research shows that the LMC may harbour a supermassive black hole that's responsible for some of the Milky Way's hypervelocity stars. Image Credit: By ESO/J. Colosimo - http://www.eso.org/public/images/potw1511a/, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=38973313

Hypervelocity stars (HVSs) were first theorized to exist in the late 1980s. In 2005, the first discoveries were confirmed. HVSs travel much faster than normal stars, and sometimes, they can exceed the galactic escape velocity. Astronomers estimate that the Milky Way contains about 1,000 HVSs, and new research shows that some of these originate in the Milky Way’s satellite galaxy, the Large Magellanic Cloud (LMC).

Does the LMC have a supermassive black hole (SMBH) that’s ejecting some HVSs into the Milky Way?

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?

March 13, 2024March 13, 2024 by Mark Thompson

Are Andromeda and the Milky Way Already Exchanging Stars?

Artist's illustration of Andromeda/Milky Way Merger. Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger

I often drag out the amazing fact that the Andromeda Galaxy, that faint fuzzy blob just off the corner of the Square of Pegasus, is heading straight for us! Of course I continue to tell people it won’t happen for a few billion years yet but a recent study suggests that we are already seeing hypervelocity stars that have been ejected from Andromeda already. It is just possible that the two galaxies have already started to exchange stars long before they are expected to merge.

November 24, 2023November 24, 2023 by Evan Gough

What Would Happen to Earth if a Rogue Star Came Too Close?

The speeding rogue star Kappa Cassiopeiae sets up a glowing bow shock in this Spitzer image (NASA/JPL-Caltech)

Stars are gravitationally fastened to their galaxies and move in concert with their surroundings. But sometimes, something breaks the bond. If a star gets too close to a supermassive black hole, for example, the black hole can expel it out into space as a rogue star.

What would happen to Earth if one of these stellar interlopers got too close?

March 23, 2023March 23, 2023 by Matt Williams

Hypervelocity Stars Teach us About Black Holes and Supernovae

An artist's conception of a hypervelocity star that has escaped the Milky Way. Credit: NASA

Hypervelocity stars (HVS) certainly live up to their name, traveling thousands of kilometers per second or a fraction of the speed of light (relativistic speeds). These speed demons are thought to be the result of galactic or black hole mergers, globular clusters kicking out members, or binary pairs where one star is kicked out when the other goes supernova. Occasionally, these stars are fast enough to escape our galaxy and (in some cases) take their planetary systems along for the ride. This could have drastic implications for our theories of how life could be distributed throughout the cosmos (aka. panspermia theory).

There are thousands of these stars in our galaxy, and tracking them has become the task of cutting-edge astrometry missions (like the ESA’s Gaia Observatory). In previous research, astronomers suggested that these stars could be used to determine the mass of the Milky Way. In a recent study from Leiden University in the Netherlands, Ph.D. candidate Fraser Evans showed how data on HVS could be used to probe the mysteries of the most extreme objects in our Universe – supermassive black holes (SMBHs) and the violent supernovae of massive stars.

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.

December 3, 2022December 3, 2022 by Evan Gough

How Do Stars Get Kicked Out of Globular Clusters?

Hubble image of Messier 54, a globular cluster located in the Sagittarius Dwarf Galaxy. Credit: ESA/Hubble & NASA

Globular clusters are densely-packed collections of stars bound together gravitationally in roughly-shaped spheres. They contain hundreds of thousands of stars. Some might contain millions of stars.

Sometimes globular clusters (GCs) kick stars out of their gravitational group. How does that work?

November 27, 2021November 27, 2021 by Brian Koberlein

Stars Getting Kicked out of the Milky Way can Help us map its Dark Matter Halo

Artist concept showing a hypervelocity star escaping our galaxy. Credit: NASA, ESA, and G. Bacon (STScI)

Dark matter is notoriously difficult to study. It’s essentially invisible to astronomers since it can’t be seen directly. So astronomers rely on effects such as the gravitational lensing of light to map its presence in the universe. That method works well for other galaxies, but not so well for our own. To map dark matter in the Milky Way, we rely mostly on the motions of stars in our galaxy. Since dark matter attracts regular matter gravitationally, the method works well for areas of the galaxy where there are stars. Unfortunately, most of the stars lie along the galactic plane, making it difficult to map dark matter above and below that plane. But a recent study proposes a way to map more of our galaxy’s dark matter using runaway stars.

January 4, 2021January 4, 2021 by Matt Williams

Astronomers Discover Hundreds of High-Velocity Stars, Many on Their Way Out of the Milky Way

Since discovering the first one in 2005, astronomers have found hundreds of stars that travel fast enough that they could escape the Milky Way as HVSs. Image Credit: NAOC/Kong Xiao

Within our galaxy, there are thousands of stars that orbit the center of the Milky Way at high velocities. On occasion, some of them pick up so much speed that they break free of our galaxy and become intergalactic objects. Because of the extreme dynamical and astrophysical processes involved, astronomers are most interested in studying these stars – especially those that are able to achieve escape velocity and leave our galaxy.

However, an international team of astronomers led from the National Astronomical Observatories of China (NAOC) recently announced the discovery of 591 high-velocity stars. Based on data provided by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and the ESA’s Gaia Observatory, they indicated that 43 of these stars are fast enough to escape the Milky Way someday.

March 15, 2019March 15, 2019 by Evan Gough

This Star has been Kicked Out of the Milky Way. It Knows What It Did.

Researchers from the University of Michigan confirm that a runaway star was ejected from the Milky Way's disk rather than the galactic core. Image Credit: Kohei Hattori

Every once in a while, the Milky Way ejects a star. The evicted star is typically ejected from the chaotic area at the center of the galaxy, where our Super Massive Black Hole (SMBH) lives. But at least one of them was ejected from the comparatively calm galactic disk, a discovery that has astronomers rethinking this whole star ejection phenomenon.