“Look, Mommy! A shooting star!”
While we all made wishes like these every once in a while as a kid, what we did not know when we were nine was that what we were seeing were actually just meteors burning up, entering Earth’s atmosphere.
But the real shooting stars are out there. And they are terrifying.
Typically depicted as being massive blue balls of gas, these giants hurtle through space across the milky way and the universe at speeds easily surpassing 1,600,000 miles per hour.
Artist’s depiction from listverse.com.
These hypervelocity stars typically originate from binary star systems that are being drawn into a black hole. As one star in the system is eaten, the other is ejected at incredible speeds, resulting in actual shooting stars.
Most of the stars found travelling within the Milky Way galaxy are coming in, and originally, scientists were stumped as to how they were mostly appearing in the Leo and Sextans constellations. Where did they come from? Why only in those areas?
A study in 2017 used data from the Sloan Digital Sky Survey, in addition to computer simulations, to find out where the stars came from. This revealed that the majority of them have actually been originating from the Large Magellanic Cloud (LMC), the largest and fasted dwarf galaxy orbiting the Milky Way. The LMC travels at around 250 miles per second (900,000 miles per hour), and the binary stars in the system travel around each other at incredible speeds. So if the system breaks up, i.e. one of the stars explode in a supernovae, then the force of the supernova would launch the other star into space as a hypervelocity star. Stars like these are so fast because they travel at the velocity at which they are ejected, plus the speed of the LMC, as that was their original velocity. The fastest stars (or, runaways, as they are called) are launched along the LMC’s orbit towards the Leo and Sextans constellations, explaining the location that these stars are usually found.
As I said, most of these stars are found coming into our galaxy, but what about the ones leaving it?
This graphic from space.com depicts the trajectories of the newly discovered stars that are leaving the galaxy, and where they are in relation to our own sun.
Most stars that are flung from the galaxy are typical hypervelocity stars that are much larger than our own sun, and are launched from the supermassive black hole in the galaxy’s center when their binary system collapses. However, these typical stars have a different composition from 20 sun-size stars discovered in 2014 that were traveling at hypervelocity speeds. This means that these stars did not originate from the galactic core, indicating that there is another, unexpected class of hypervelocity star that relies on an ejection mechanism from the one that holds our galaxy together.
In conclusion, much more research is to be done to discover more about these stars that travel practically faster than we can comprehend. But in the meantime, let’s keep wishing on meteors.