In this illustration of an ultra-luminous X-ray source, two rivers of hot gas are pulled onto the surface of a neutron star. Strong magnetic fields, shown in green, may change the interaction of matter and light near neutron stars’ surface, increasing how bright they can become.Credits: NASA/JPL-Caltech
Something in outer space is breaking the law, that is, the laws of physics. Astronomers call these lawbreakers ultraluminous X-ray sources (ULX), and they exude around 10 million times more energy than the sun. This amount of energy breaks a physical law known as the Eddington limit, which determines how bright something of a given size can be. If something breaches the Eddington limit, scientists expect it to blow apart. However, ULXs “regularly exceed this limit by 100 to 500 times, leaving scientists baffled,” according to a NASA statement (opens in a new tab).
New observations published in The Astrophysical Journal (opens in a new tab) from NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), which views the universe in high-energy X-rays, confirmed that one ULX in particular, named M82 X- 2 is definitely too bright. Previous theories suggested that the extreme brightness could be some kind of optical illusion, but this new work shows that’s not the case: this ULX is actually defying the Eddington limit in some way. Astronomers used to believe that ULXs could be black holes, but M82 X-2 is an object known as a neutron star. Neutron stars are the remains of the dead cores of stars like the sun. A neutron star is so dense that gravity at its surface is about 100 trillion times stronger than Earth’s. This intense gravity means that any material thrown onto the dead star’s surface will have an explosive effect
.”A marshmallow dropped onto the surface of a neutron star would hit it with the energy of a thousand hydrogen bombs,” according to NASA (opens in a new tab). The new study found that M82 X-2 consumes about 1.5 Earths worth of material each year, drawing it from a neighboring star. When this amount of matter hits the surface of the neutron star, it’s enough to produce the unusual glow that astronomers observed. The research team believes this is evidence that something must be going on with M82 X-2 that allows it to break the rules and break the Eddington limit. His current idea is that the neutron star’s intense magnetic field changes the shape of its atoms, allowing the star to hold together even as it grows brighter and brighter.
“These observations allow us to see effects of these incredibly strong magnetic fields that we could never reproduce on Earth with current technology,” said the study’s lead author. Mateo Bachetti (opens in a new tab), an astrophysicist at the Cagliari Astronomical Observatory in Italy, said in the statement. “This is the beauty of astronomy…we can’t really set up experiments to get quick answers; we have to wait for the universe to show us its secrets.”