Peering into the heart of the Milky Way , astronomers have spotted the 'howls ' of dead stars as they feed on stellar companions . These zombie stars are thought to be leaving a 'mass grave ' of white dwarf stars near the centre of the Milky Way . But why there are so many of these stars here - which are left behind when a larger star runs out of fuel - remains a mystery . Scroll down for video . The Nuclear Spectroscopic Telescope Array , or NuStar , has captured a new high-energy X-ray view ( magenta ) of the bustling center of our Milky Way galaxy . The smaller circle shows the center of our galaxy where the NuStar image was taken . The finding , published in Nature , was made by scientists at Haverford College in Pennsylvania , US using Nasa 's NuStar telescope . 'We can see a completely new component of the centre of our galaxy with Nustar 's images , ' said Kerstin Perez of Columbia University in New York . 'We ca n't definitively explain the X-ray signal yet - it 's a mystery . More work needs to be done . ' When a star runs out of fuel it usually collapses in on itself . Stars more than eight times the mass of our sun will explode in a supernova , leaving behind a neutron star or black hole . Smaller stars , though , will shed their outer layers and leave behind a hot dense core – known as a white dwarf . A white dwarf contains a similar amount of mass to its previous star but will be much smaller – about the size of Earth – making gravity at its surface much more intense . They are thought to be able to burn for tens or hundreds of billions of years - at which point they become black dwarfs – but as the universe is not this old , no black dwarfs exist in the universe yet . When they peered at the Galactic Centre , they found an emission of X-rays that corresponded to thousands of dead stars being present . The emission could also be due to millisecond pulsars - rapidly rotating neutron stars - or dense magnetic fields . 'However , all these interpretations pose significant challenges to our understanding of stellar evolution , binary formation and cosmic-ray production in the Galactic Centre , ' the researchers wrote in their paper . The emissions were found to be coming from a region of the Galactic Centre 13 by 26 light-years in size around the central supermassive black hole , called Sagittarius A* . On theory is that when stars die , they do n't always go quietly into the night . Unlike stars like our sun , collapsed dead stars that belong to stellar pairs , or binaries , can siphon matter from their companions . This zombie-like 'feeding ' process differs depending on the nature of the normal star , but the result may be an eruption of X-rays . But it is the potential for these to be white dwarf stars that is the most intriguing theory . Scientists at Haverford College in Pennsylvania say they have spotted X-ray emissions consistent with thousands of white dwarfs ( one illustrated centre ) at the galaxy 's centre . These are stars left behind after larger ones use up their fuel . But why thousands of these stars are here remains a mystery . There are already known to be many young , massive stars orbiting our galaxy 's central supermassive black hole - but why there would be thousands of white dwarf stars as well is not clear . White dwarfs are what are left when medium-mass stars - including our sun - shed their outer layers at the end of their life . Behind is left the hot , dense core which burns white . If the white dwarf gathers too much material from a companion , its mass will reach a critical point and the star will explode . The researchers say the latest finding needs further study to get to the bottom of the mystery . 'This new result just reminds us that the galactic center is a bizarre place , ' said co-author Chuck Hailey of Columbia University . 'In the same way people behave differently walking on the street instead of jammed on a crowded rush hour subway , stellar objects exhibit weird behavior when crammed in close quarters near the supermassive black hole . ' Shown is the region around the supermassive black hole at the Milky Way 's Galactic Centre - Sagittarius A* - where the X-ray emissions consistent with thousands of white dwarfs were found . Other possible explanations include millisecond pulsars , which are rapidly rotating neutron stars . Nasa 's NuStar telescope ( illustrated ) is a space-based X-ray telescope that focuses high-energy X-rays from distant astrophysical sources . Its primary goal is to conduct a survey for black holes , but it has also been used for other purposes such as this latest research .
Scientists at Haverford College in Nature made the finding . They spotted X-ray emissions consistent with thousands of white dwarfs . These are stars left behind after larger ones use up their fuel . But why thousands of these stars are there remains a mystery .