Hypervelocity Starry Night

Published on August 7, 2017 by Regan Green  

Data collected by the European Space Agency’s Gaia spacecraft will soon be applied to create the world’s largest and most precise 3D astronomical map. Launched in 2014, Gaia has spent the past three years gathering information on the cosmos for this map.

A particularly significant discovery that Gaia has made is the existence of six new hypervelocity stars in the Milky Way. One of the stars is moving so rapidly that it might even exit our galaxy! Here’s how that works: hypervelocity stars are ultrafast stars that can move up to a few hundred miles per second above average. Their extraordinary speeds are caused by close stellar encounters or supernova explosions. If a star reached a high enough speed, it will become gravitationally unbound to its home galaxy and will be able to journey into another.

Scientists take a special interest in hypervelocity stars because they tell us more about the galaxy’s history. Elena Maria Rossi of Leiden University comments on this matter, “These are stars that have traveled great distances through the Galaxy but can be traced back to its core – an area so dense and obscured by interstellar gas and dust that it is normally very difficult to observe – so they yield crucial information about the gravitational field of the Milky Way from the centre to its outskirts.”

However, finding these stars has been extremely difficult due to their high velocities. Because of this, the team at Leiden University took a different approach. They began to use a machine learning algorithm to search through Gaia’s data. Team member Tommaso Marchetti explains it this way: “In the end, we chose to use an artificial neural network, which is software designed to mimic how our brain works. After proper ‘training’, it can learn how to recognize certain objects or patterns in a huge dataset. In our case, we taught it to spot hypervelocity stars in a stellar catalogue like the one compiled with Gaia.” Within the first hour of using this method, the number of potential hypervelocity stars in the dataset had been reduced to about 1% of its original body, bringing it down to 20,000 candidates. After an adjustment, the number was reduced to a mere 80. The team then individually studied the 80 stars, eventually concluding that six were hypervelocity stars.

The most important takeaway from this experience is that these new six stars are not as large as the twenty hypervelocity stars previously discovered, which were all comparable in size to our sun. Moreover, scientists are curious as to why the six slower stars seem to have been slowed down at some point and theorize that a past interaction with dark matter may be responsible.

The team is updating their program now to be able to take on a much larger data set and its release date is set for April of 2018! #GetExcitedSU!

Video credit: ESA/Gaia/DPAC