2023-04-11 19:49:16
NASA’s NuSTAR space observatory has confirmed that ultraluminous X-ray sources (ULX) cosmic rays are as bright as they appear and exceed the Eddington limit.
This is the point at which the luminosity emitted by an active star or galaxy it is so extreme that it begins to push out the outer layers of the object. These X-ray sources regularly exceed this limit, which limits an object’s brightness as a function of its mass, by 100 to 500 times, leaving scientists baffled.
The research, published in The Astrophysical Journal, suggests that this boundary-breaking glow is due to the strong magnetic fields of the ULX. But scientists can test this idea only through observations: Up to billions of times more powerful than the strongest magnets ever made on Earth, ULX magnetic fields cannot be reproduced in a laboratory.
Eddington limit
Particles of light, called photons, exert an little push on the objects they find. If a cosmic object like an ULX emits enough light, the outward pull of photons can overcome the inward pull of the object’s gravity. When this happens, an object has Eddington limit reached and, in theory, the light of the object it will push any gas or other material that falls towards it.
That change, when light overcomes gravity, is significant, because the material falling on an ULX is the source of its glow. This is something that scientists often seen in black holes: When stray gas and dust are pulled in by their strong gravity, those materials can heat up and radiate light. Scientists used to think that ULXs they must be black holes surrounded by glowing caskets of gas.
But in 2014, data from NuSTAR (Nuclear Spectroscopic Telescope Array) revealed that an ULX with the name of M82 X-2 is actually a less massive object called a neutron star. Like black holes, neutron stars form when a star dies and collapses, packing more than the mass of our Sun into an area not much larger than an average-sized city.
This incredible density also creates a gravitational pull on the surface of the neutron star about 100 trillion times stronger than the gravitational pull on the Earth’s surface. The gas and other materials dragged by that gravity accelerate to millions of miles per hour, releasing tremendous energy when they hit the surface of the neutron star. (A marshmallow falling on the surface of a neutron star would hit it with the energy of a thousand hydrogen bombs.) This produces the high-energy X-ray light that NuSTAR detects.
The recent study took aim at the same ULX at the heart of the 2014 discovery and found that, like a cosmic parasite, M82 X-2 is stealing around de 9 trillion trillion tons of material per year from a neighboring star, or about one and a half times the mass of the Earth. Knowing how much material hits the neutron star’s surface, scientists can estimate how bright the ULX should be, and their calculations match independent measurements of its brightness. The work confirmed that M82 X-2 exceeds the Eddington limit, NASA reports.
future of find
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If the scientists can confirm the brightness of more ULX, can confirm a persistent hypothesis that would explain the apparent brightness of these objects without the ULX having to exceed the Eddington limit. That hypothesis, based on observations of other cosmic objects, postulates that strong winds form a hollow cone around the light source, concentrating most of the emission in one direction. If pointed directly at Earth, the cone could create a kind of optical illusion, falsely making it appear as if the ULX is exceeding the brightness limit.
Even if that’s the case for some ULXs, an alternative hypothesis supported by the new study suggests that strong magnetic fields distort the atoms roughly spherical in elongated, fibrous shapes. This would reduce the ability of photons to push atoms away, and ultimately increase the maximum possible brightness of an object.
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