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A mysterious ring of radio gentle may have been created by a sort of large star with a strong wind of radiation blowing away its outer layers, based on astronomers who made the invention with the MeerKAT radio telescope in South Africa.
In 2019, astronomers conducting a survey with the Australian Sq. Kilometer Array Pathfinder telescope, or ASKAP, seen a number of unusual rings of radio gentle, undetectable at another wavelength of sunshine and with no apparent supply. The astronomers referred to as them ‘odd radio circles’, or ORCs for brief.
Solely a handful are at present identified, however now a brand new ORC has been found that breaks all the foundations.
ASKAP is a technological precursor to the Square Kilometer Array (SKA), which might be an enormous array of radio dishes and antennas cut up between Australia and South Africa. So it is becoming that South Africa additionally has its personal SKA precursor observatory, within the type of MeerKAT, initially the Karou Radio Telescope, based mostly within the nation’s Meerkat Nationwide Park.
It was in observations made with MeerKAT in November 2022 that astronomers led by Cristobal Bordiu of Catania Observatory in Italy noticed one thing out of the peculiar. It was an ORC, however it’s not the place it’s speculated to be.
Previous to this discovery, all earlier ORCs had been discovered at excessive galactic latitudes. In different phrases, they’re excessive above the aircraft of our Milky Way galaxy, which means that they’re both very near us inside our galaxy, or they’re extragalactic. Certainly, a number of ORCs comprise a galaxy in the course of the ring, and people ORCs are thought to have been produced by an outburst from that galaxy, maybe from a starburst occasion leading to lots of supernovas, or a merger between two supermassive black holes leading to a pulse of power.
This new ORC, nevertheless, is simply six levels above the aircraft of our galaxy, slap bang within the Milky Means as introduced on the sky. Moreover it seems, from our standpoint, to be fairly near the galactic heart. Nonetheless, that would simply be a coincidence — it might be a lot nearer, or a lot farther away, than the middle of our galaxy, which is 26,000 light-years away.
The ORC, cataloged as J1802–3353, has been nicknamed Kýklos by its discoverers, a phrase meaning circle in Greek. Kýklos spans 80 arcseconds within the sky — one arcsecond is 1/3,600th of a level. The ring itself is barely seen at radio wavelengths, the place it’s faint, patchy, skinny (simply 6 arcseconds thick) and nearly an ideal circle. Its radio spectrum is surprisingly flat, which means that it does not have any notable spectral strains in contrast to earlier ORCs.
Bordiu’s group realized that this ORC might be one thing new, however earlier than they might decide that, they needed to rule out the opposite prospects.
The European House Company’s Gaia mission has cataloged three galaxies that each one occur to lie inside Kýklos on the sky. One galaxy specifically is simply 3 arcseconds from the middle of the ring, but when Kýklos was produced by this galaxy then explaining why it has such a flat spectrum in comparison with different ORCs linked to galaxies can be a problem.
If Kýklos is just not extragalactic, then it should be in our Milky Means galaxy, which suggests a stellar origin. Supernova remnants are sometimes spherical nebular constructions produced by the blast wave from an exploding star colliding with the fuel and dirt within the interstellar medium.
Nonetheless, supernova remnants often produce X-rays too, and no X-rays have been detected coming from Kýklos. Though a number of pulsars, that are spinning neutron stars created by some supernovas, have been detected contained in the ring from our standpoint, we’ve got no distance details about them to say whether or not they’re linked to the ring or whether or not their location is merely a line-of-sight coincidence.
Maybe Kýklos is a planetary nebula, which is the cast-off envelope of a dying sun-like star. A planetary nebula often grows to about 3 light-years broad earlier than dispersing; if Kýklos have been a planetary nebula it should be an abnormally giant one, or be moderately near us, to look 80 arcseconds broad within the sky. (For comparability, probably essentially the most well-known planetary nebula is the Ring Nebula within the constellation of Lyra, which is 230 arcseconds broad at a distance of two,200 light-years.) Nonetheless, a planetary nebula produces optical emission, particularly in hydrogen-alpha gentle, however no such gentle has been detected.
As a substitute, maybe the ring has been produced by a large, unstable star, particularly a Wolf–Rayet star. As a result of a Wolf–Rayet star is so large, it is ready to generate a strong wind of radiation that blows its outer layers deep into house, lowering its mass and making it extra secure. Wolf–Rayet stars are sometimes acknowledged both by way of the nebula that they blow, or by their composition — with their hydrogen envelope forged adrift, the heavier parts corresponding to helium and oxygen inside their deeper layers are uncovered.
Though no Wolf–Rayet nebula is clear inside Kýklos, this isn’t an issue since a Wolf–Rayet star’s quick radiation wind shortly destroys the dusty nebula near it. Colder mud farther out would survive and radiate at 24 microns, however Bordiu’s group level out that there isn’t any information accessible at this wavelength to have the ability to say whether or not this colder mud is current or not. Nonetheless, there’s different proof to assist the Wolf–Rayet star situation, which is the flat spectrum that may be very typical of any such star shedding mass.
“Based mostly on the restricted information at present accessible, the morphological and spectral traits of Kýklos seem extra in keeping with these of a Wolf–Rayet shell,” Bordiu’s group wrote of their analysis paper.
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It’s true {that a} Wolf–Rayet star has not but been recognized inside Kýklos but. There may be one vivid star, HD 164455, however it isn’t a Wolf–Rayet star. Gaia has recognized three different stellar candidates, together with one bluish star that’s 24,500 gentle years away from us. If that is the supply of Kýklos, then at that distance the ring can be about 10 light-years throughout. Nonetheless, there isn’t any spectral information on this star to say whether or not it’s a Wolf–Rayet star or not.
The following step, due to this fact, might be to comply with up with the James Webb Space Telescope and acquire that information to probably resolve the thriller of Kýklos.
The findings have been accepted for publication within the journal Astronomy & Astrophysics, and a preprint model is obtainable on arXiv.
