Hypervelocity Stars

In 2005, the first hypervelocity star (HVS) was discovered by Smithsonian astronomers. These objects are defined as stars with very high velocities compared to normal star velocities in a galaxy. Some of them have velocities that exceed the escape velocity of the galaxy. They are thought to originate from encounters of binary stars with the supermassive black hole at the center of the Milky Way Galaxy. One of the partners of the binary star is “captured” by the black hole, entering orbit around it, while the other partner escapes with a high velocity to become an HVS. In addition to the black hole origin of HVSs, it is also thought that HVSs can be induced by supernovas. In this case, a HVS is ejected from a binary system when the other partner undergoes a supernova explosion.

Diagram Showing Star Ejection from a Galaxy

As of 2014, there are 20 known HVSs. These HVSs all have masses a few times that of the Sun, though dwarf HVS candidates have also been discovered. There are so few confirmed HVSs because they are pretty difficult to track down. It’s not easy to search through a billion stars and find a couple that are moving abnormally. In order to locate them successfully, astronomers have used a specific type of telescope to focus on a large group of stars on the edges of the Milky Way’s black hole that had traveled a notable distance. They then were able to narrow down this large group to stars that were travelling at speeds consistent with ejection from the center of the Milky Way. Once we learn more about HVSs, we can use information about them to learn about stars that form in the centers of galaxies and the sizes of black holes at the centers of galaxies.

This link from Harvard contains a complete collection of links to general information, podcasts, scientific publications, and other links about hypervelocity stars. This article serves as a good introduction to the topic.

2 thoughts on “Hypervelocity Stars

  1. W. H. O. A. That’s crazy that there are stars moving with such large velocities in our own galaxy, and even more interesting that they can exceed the escape velocity of the galaxy, because I know that it is much larger than that of our solar system’s escape velocity.

    Still, it is pretty terrifying to consider that there could be solar systems that are not bound to any galaxy hurtling rapidly out in the middle of nowhere; just imagine if our own solar system were like that. I think it would maybe make humanity feel more special, but also more aware of its fragility.


  2. I wonder how far HVS have gotten from the center of the Milky Way. Must be a long trip, to get ejected from the galaxy. Keith’s thoughts first made me curious whether an HVS could be used as something of a gravitational spaceship to provide energy while a satellite of human’s hitchhike across the galaxy. But Jordyn’s suggested primer says that HVS travel at over 200 million MPH, so it would probably be best to just get out of their way.


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