A strange, rare space explosion seen where it shouldn’t be: ScienceAlert

We may know much less about a strange kind of cosmic explosion than we thought.

They are known as Luminous Fast Blue Optical Transients, or LFBOTs, and one of them is named Finch (AT2023fhn) were observed in intergalactic space, at a great distance from the nearest galaxy.

That’s a problem, because astronomers thought LFBOTs could be a type of massive supernova — something that’s actually thought to only happen within the confines of a galaxy.

“The more we learn about LFBOTs, the more they surprise us.” says astronomer Ashley Krems European Space Agency and Radboud University in the Netherlands.

“We have now shown that LFBOTs can occur at a long distance from their nearest galaxy, and Finch’s location is not what we would expect for a supernova.”

The first LFBOT was spotted in 2018, and since then we’ve spotted about a handful of it. With each new discovery, LFBOT continued to puzzle scientists. These space explosions are extremely bright — at least 10 times brighter than a normal supernova — and extremely short.

Ordinary supernovae tend to flare to their peak, then fade away over weeks or months; LFBOTs are like camera flashes in space. And it’s very hot. This is what gives them a bluish color.

Scientists thought these events might have been caused by an unusual type of supernova collapse, in which the core of a dying star collapses directly into a neutron star or black hole. This would require a massive progenitor star, At least eight times the mass of the Sun.

Another possibility is that the flashes could be caused by a black hole devouring another ultra-dense object, such as an object White dwarf star.

Massive stars don’t live long Main sequence Spirits. that it Less than 100 million years ago A star with a mass eight times the mass of the Sun. They are born in areas very rich in dense gas and dust, which means galaxies. there There is not much matter in intergalactic space.

Although some stars can be ejected from orbit onto an escape path and speed out of host galaxies, massive neutron stars and progenitors of black holes are not expected to get that far before supernovas eventually appear.

In fact, all previous LFBOTs were discovered in the spiral arms of galaxies where star formation occurs, which is the expected place to observe a supernova.

This brings us to Finch’s problem. It was discovered by the Zwicky Transient Facility on April 10, 2023. Its temperature was measured at 20,000 degrees Celsius (about 36,000 Fahrenheit). Hubble was then called in to find out its source. This is where things start to get a little weird.

The explosion occurred about 2.86 billion light-years away, but in intergalactic space, about 50,000 light-years from the nearest spiral galaxy, and 15,000 light-years from the nearest dwarf galaxy belonging to that spiral galaxy. This poses a major challenge to the supernova hypothesis.

But the black hole hypothesis is still on the table. Researchers say it’s possible that an ancient, isolated ball of stars known as a globular cluster lurks in intergalactic space.

Globular clusters are thought to be full of black holes, of the rarely seen intermediate mass variety. If there’s a globular cluster out there, too faint to see, we’ve probably caught one of these black holes feeding uncontrollably.

Another possibility is that the explosion was the result of a collision between two neutron stars, one of which could be a magnetar, whose intense magnetic field could have amplified the resulting kilonova. Theoretical analysis will need to be conducted to determine the plausibility of this scenario.

“The discovery raises more questions than it answers.” says Krems. “More work is needed to find out which of the several possible explanations is correct.”

One thing is certain, though. The more of these things we find, the stranger they become.

The research was accepted in Monthly Notices of Letters of the Royal Astronomical Societyand is available on arXiv.