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Oct 23rd 2019

Five Strange Stars That Keep Astronomers on Their Toes

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On a moonless night, far from city lights, the sky seems filled with countless stars. And of course the stars we can see, even on the darkest and clearest night, are only a tiny fraction of the total: billions of galaxies, each with billions of stars.

Most of these stars have characteristics that are familiar to astronomers, and their lives unfold in fairly predictable ways. In the case of our sun, this is very good news for us. But there are also some decidedly strange stars out there.

Some pose mysteries for astronomers; others are not so much puzzling as they are just plain awesome. All of them come in handy when you want to entertain your friends with some interesting space facts.

Zombie Stars

Supernova explosions, disintegrating stars that briefly flare up to several hundred million times brighter than the sun, ought to have the ring of finality if anything does. But Science Alert reports that astronomers have now discovered several cases of zombie stars that underwent supernova explosions yet somehow managed to reassemble themselves and go on shining. Strange stars don’t get much stranger than that.

The name might seem a bit unfair. After all, while these certainly qualify as strange stars, there is no evidence that they resemble zombies. Surely “supernova survivor” would be just as accurate. But zombie stars don’t just reanimate after going supernova — they do so by dining on other stars, gravitationally stripping them away until nothing is left of the other star. So perhaps the name fits!

A New Alien Megastructure Candidate

Astronomers sometimes observe objects that seem to be fairly ordinary stars, except that their light output seems to vary in ways that are completely inexplicable.

A familiar recent example was a star officially named KIC 8462852, better known as Tabby’s Star, after the astronomer who investigated it. Its light patterns are so strange that Tabetha Boyajian and other astronomers seriously considered the possibility that it was surrounded by an artificial structure. Alas, further observations were not consistent with this theory, and mere dust clouds are a more likely culprit.

But there is a new kid in town among strange stars, HD 139139. It has not yet acquired a popular name, but as Scientific American reports, the astronomers are still scrambling to come with a robust explanation for what they are seeing. A megastructure, perhaps?

The Methusaleh Star

One of the most interesting space facts concerns HD 140283, named the Methusaleh star after the biblical figure. Classified as a subgiant, the Methusaleh star is fairly normal, not what you’d expect in a list of strange stars — except for one subtle but serious complication. Observations of HD 140283 indicate that, according to our understanding of stellar aging, it ought to be between 13.2 and 14.4 billion years old. The hitch is that, as NASA points out, by our best estimate the entire universe is about 13.8 billion years old.

This rules out the upper half of the age range for HD 140283, and makes even the low-end estimate seriously problematic. How can such an ordinary star have been formed when the universe itself was only just starting to take shape? A good question, and cosmologists would love to know the answer.

A Baby Star That Will Outlive the Sun

If the Methusaleh star is unusually old for a star, a dim nearby star designated 2MASS J0523-1403 is in its merest infancy — and will be for billions of years to come, long after our sun has flared into a red giant, then dwindled away.

There is no particular mystery here, just a sheer breadth of time that sends shivers up the spine. 2MASS J0523-1403, according to a report in Scientific American, is very close to the dividing line between the smallest and least massive red dwarf stars and their slightly smaller and less massive cousins, brown dwarfs — objects that are not quite full-blown stars, because they are not big enough to sustain hydrogen fusion.

Small as it is, 2MASS J0523-1403 is a true star that does burn hydrogen — and will go on burning it for an estimated 12 trillion years, long after the sun has become a tiny dark cinder.

The Most Massive Star in the Universe

At the far end of the stellar mass and brightness range from 2MASS J0523-1403 is a star known as R136a1, and located approximately 170,000 light-years away in the Milky Way’s largest satellite galaxy, the Large Magellanic Cloud. According to NASA, R136a1 is the most massive known star.

In cosmic terms, R136a1 will not shine for long. Stars of this type are headed for supernova explosions, says EarthSky, and that should be the end of it. Unless, perhaps, it becomes a zombie star, and comes back for another round.

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