Astronomers have discovered a bizarre cosmic object that shines millions of times brighter than the sun, breaking a physical law known as the Eddington limit. The object is an ultraluminous X-ray source (ULX), a type of exotic cosmic object that produces about 10 million times more energy than the sun.
The Eddington limit is a theoretical limit that determines how bright something of a given size can be. If something breaks the Eddington limit, it should blow itself up into pieces. However, ULXs regularly exceed this limit by 100 to 500 times, leaving scientists puzzled.
The new study, published in The Astrophysical Journal, used NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), which sees the universe in high-energy X-rays, to confirm that one particular ULX, called M82 X-2, is definitely too bright. Previous theories suggested that the extreme brightness could be some sort of optical illusion, but this new work shows that’s not the case — this ULX is actually defying the Eddington limit somehow.
The study also revealed that M82 X-2 is not a black hole, as astronomers used to believe, but a neutron star. Neutron stars are the leftover, dead cores of stars like the sun. They are so dense that the gravity on their surface is about 100 trillion times stronger than that of Earth. This intense gravity means that any material pulled onto the dead star’s surface will have an explosive effect.
The research team found that M82 X-2 consumes around 1.5 Earths’ worth of material each year, siphoning it off of a neighboring star. When this amount of matter hits the neutron star’s surface, it’s enough to produce the off-the-charts brightness the astronomers observed.
The researchers think this is evidence that something must be going on with M82 X-2 that lets it bend the rules and break the Eddington limit. Their current idea is that the intense magnetic field of the neutron star changes the shape of its atoms, allowing the star to stick together even as it gets brighter and brighter.
“These observations let us see the effects of these incredibly strong magnetic fields that we could never reproduce on Earth with current technology,” lead study author Matteo Bachetti, an astrophysicist at the Cagliari Astronomical Observatory in Italy, said in a NASA statement.
The study also opens up new possibilities for understanding ULXs and other extreme cosmic phenomena.
“This discovery shows us that there are still many surprises out there waiting for us,” co-author Fiona Harrison, a professor of physics and astronomy at Caltech and principal investigator of NuSTAR, said in the statement. “We need to keep looking for these strange and exotic objects to learn more about how our universe works.“
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