Patches of bright blue and green light in the Fireworks Galaxy NGC 6946 show areas of X-ray concentrations captured by the NASA NuSTAR satellite. These X-ray sources, created by some of the Universe’s most powerful processes, are extremely rare. NASA is now exploring the possibility the surprise light appearance was emitted by a black hole consuming another object, such as a star.
NASA’s NuSTAR satellite’s primary objective is to study supernova, the explosion of star even more enormous than our Sun.
Ten days is a really short amount of time for such a bright object to appear
These cosmic explosions appear as a bright blue-green spot at upper right corner.
These extreme events can briefly spew enough visible light to outshine entire galaxies consisting of billions of stars.
They also generate much of the chemical elements in our universe are heavier than iron.
The green blob was not visible during initial NASA NuSTAR images but was burning bright during a second observation only days later.
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NASA news: A satellite spots a mysterious green light that quickly disappeared (Image: NASA)
NASA news: The NuSTAR X-ray observatory spotted a strange sight in the Fireworks galaxy (Image: Getty)
NASA’s Chandra X-ray Observatory later observed that the source, an ultra-luminous X-ray source (ULX), had swiftly disappeared.
The object was dubbed ULX-4 because it is the fourth ULX identified in this galaxy.
No visible light was detected with the X-ray source, a fact likely ruling-out the possibility it is also a supernova.
Hannah Earnshaw, a postdoctoral Caltech researcher, and lead author on the new study, said: “Ten days is a really short amount of time for such a bright object to appear.
“Usually with NASA NuSTAR, we observe more gradual changes over time, and we don’t often observe a source multiple times in quick succession.
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“In this instance, we were fortunate to catch a source changing extremely quickly, which is very exciting.”
When an object gets too close to a black hole, gravity can pull that object apart, bringing the debris into a close orbit around the black hole.
Material at this newly-formed disk’s inner edge starts moving so fast it heats up to millions of degrees and radiates X-rays.
The surface of the Sun, by comparison, is about 5,500C (10,000F).
Most ULXs are usually long-lived because they are created by a dense object, like a black hole, devouring a star for an extended period of time.
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NASA news: Black holes are one of the Universe’s most extreme entities (Image: Getty/Express)
Short-lived, or “transient,” X-ray sources like ULX-4 are far more rare, meaning a single dramatic event – such as a black hole swiftly annihilating a small star – could explain the observation.
However, ULX-4 might not be a one-off event, and NASA has explored other potential explanations for this object.
One possibility for ULX-4 might be a neutron star – extremely dense objects formed from the explosion of a star not large enough to form a black hole.
Boasting the same mass as our Sun but squeezed into an object the size of a city, neutron stars can, like black holes, draw in material and create a fast-moving disk of debris.
These can also generate slow-feeding ultra-luminous X-ray sources, although the X-ray light is produced through slightly different processes than in ULXs created by black holes.
NASA news: It is possible the light was from a black hole consuming another object like a star (Image: Getty)
Neutron stars create magnetic fields powerful enough to create “columns” channel material down to the surface, generating powerful X-rays in the process.
But if the neutron star spins especially fast, those magnetic fields can create a barrier, making it impossible for material to reach the star’s surface.
“It would kind of be like trying to jump onto a carousel that’s spinning at thousands of miles per hour,” said Earnshaw.
The barrier effect would prevent the star from being a bright source of X-rays except for those times when the magnetic barrier might waver briefly, allowing material to slip through and fall onto the neutron star’s surface. This could be another possible explanation for the sudden appearance and disappearance of ULX-4. If the same source were to light up again, it might support this hypothesis.
Ms Earnshaw tweeted: “We do sometimes see large and fast transitions between bright and faint states in ultraluminous X-ray sources that are neutron stars – when the spinning magnetic field is fast and powerful enough to stop matter from accreting on the object and thus dimming it.”