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Artist concept of Wide Field Infrared Survey Explorer orbiting the Earth. Credit: NASA / JPL
Our universe is capable of really scary scenarios, and in this case, we have an apparent tragedy: two stars, companions for life, decide together to move away from the galaxy of the Milky Way. But after millions of years of adventures in intergalactic space, one star kills and consumes the other. He is now pursuing his journey through the universe alone, much brighter than before, surrounded by a shell of leftover remains.
At least we think. All we need to do now is a crime scene.
Investigating.
The case of the Too-Young star
The name of the star is quite modest, even if it is a little obscure: CPD 64 ° 2731. And at first glance, it is not particularly strange, with a mass of about forty times that of the sun. But his circumstances are downright odd. It is incredibly fast, at 160 km / s. It is well outside the Milky Way galaxy, about 25,000 light-years away from us and about 2,000 light-years away from the galactic disk. And it runs incredibly fast, at over 300 kilometers per second (compared to the relatively quiet speed of 2 kilometers per second for the sun).
It got worse. Recent observations made by a team using the Wide Field Explorer Infrared Survey paint a portrait of a thin horseshoe-shaped gas and dust shell surrounding this radical star, the shell itself being illuminated by the intense radiation of the stellar surface.
And here is the strangest part. Assuming that the star was born somewhere in the Milky Way drive (a fairly safe bet), it would have taken about six million years to reach its current position outside the galaxy. But a star of this size, mass, and temperature should only be three million years old.
The shock in the arc of Zeta Ophiuchi, another star on the run observed by Spitzer. Credit: NASA / JPL-Caltech
Something is wrong.
Chased from the city
Something chased CPD 64 ° 2731 from the galaxy, and it was probably his closest friends and neighbors. Stars tend to be born in groups and clusters, from tens to hundreds, emerging from the same molecular cloud. In most cases, these stars move apart slowly as an open cluster and become more independent as they age.
But fortuitous encounters can have detrimental effects on this serene expansion. When three or more stars of comparable mass come closer, their gravitational interactions become incredibly unstable. In some cases, they slightly modify their trajectory but do not remain affected. In others, they capture and form long – term orbits. But from time to time, the energies add up in a totally erroneous way, sending one or more stars to fly away completely at ridiculous speeds.
This is how the so-called "fleeing stars" get their momentum and once launched, nothing holds them back. In many cases, they are quite on an exit trajectory from the galaxy, as in the case of our enigmatic friend, CPD 64 ° 2731.
And in situations where stars are born close enough to each other to become runaways, many of these stars are binary systems.
Ah, a clue.
This artist's impression shows the VFTS 352 – the most powerful and massive double-star system to date, where both components are in contact and share materials. The two stars of this extreme system are about 160,000 light-years from Earth in the Great Magellanic Cloud. This intriguing system may well have a dramatic end, either with the formation of a single giant star or as a future black binary hole. Credit: ESO / L. Calçada
The killer companion
Sometimes the stars eat their companions. If one of the two gets too close, the more massive sucks the gas from the nearby atmosphere like a stellar vampire. And as you can imagine, once this scenario begins to play, it is usually not very well finished – the stars are not very sweet to destabilize their atmospheres. Flares, rashes and tantrums ensue.
In the worst case, the pair becomes so destabilized that its orbits narrowed and narrowed, eventually fusing the stars into a terrible – and fatal – embrace. Needless to say, this process releases an enormous amount of energy, capable of blowing into the space surrounding a multitude of dense suns, into a gigantic nebula.
The newly combined star (if it survives at all) completely changes character. He will now spin quickly with the absorption of all that juicy angular momentum of his mate once in orbit. Thanks to its unlucky host, it now has a new raw fuel supply, as well as a substantial increase in its mass, thus increasing its melting rate and its radiation. And this output of pumped radiation illuminates the surrounding nebula like a neon sign.
The end result of such a fantastic collision? A single giant star, which rotates quickly, is reconstituted and reborn in his youth, surrounded by the remains of the violent encounter with his twin.
And in this case, as a recent article assumes, a perfidious star comes out of his native galaxy, free but still fleeting.
Explore further:
The fastest stars of the Milky Way are "runaways" from another galaxy
More information:
V. V. Gvaramadze et al. CPD-64 2731: a shooting star at high speed and regenerated. arXiv: 1810.12916 [astro-ph.SR]. arxiv.org/abs/1810.12916
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