- 3689 - MAGNETARS and MASERS - For the first time, astronomers have definitively spotted a flaring “magnetar” in another galaxy. These ultra-magnetic stellar corpses were thought to be responsible for some of the highest-energy explosions in the nearby universe. But until this burst, no one could prove it.
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- The first sign of this magnetar arrived as a blast of X-rays and gamma rays. Five telescopes in space, including the Fermi Gamma-ray Space Telescope and the Mars Odyssey orbiter, observed the blast, giving scientists enough information to track down its source: the galaxy NGC 253, or the Sculptor galaxy, 11.4 million light-years away.
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- At first, astronomers thought that the blast was a type of cataclysmic explosion called a short “gamma-ray burst“, or GRB, which are typically caused by colliding neutron stars or other destructive cosmic events. But the signal looked weird for a short GRB: It rose to peak brightness quickly, within two milliseconds, tailed off for another 50 milliseconds and appeared to be over by about 140 milliseconds. As the signal faded, some of the telescopes detected fluctuations in the light that changed faster than a millisecond.
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- Typical short GRB’s that result from a neutron star collision don’t change like that. But, flaring magnetars in our own galaxy do, when the bright spot where the flare was emitted comes in and out of view as the magnetar spins.
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- Then, surprisingly, the Fermi telescope caught gamma rays with energies higher than a giga-electronvolt arriving four minutes after the initial blast. There is no way for the known sources of short GRBs to do that.
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- A flaring magnetar sent a blast of light and particles zipping through space. The interaction between those particles and the environment around the magnetar could help explain the blast’s strange appearance. The flare may be triggered by a massive “star quake“, one thousand trillion trillion, or 10^27, times as large as the 9.5 magnitude earthquake recorded in Chile in 1960.
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- The quake led the magnetar to release a blob of plasma that sped away at nearly the speed of light, emitting gamma rays and X-rays as it went. This discovery suggests that at least some signals that look like short GRBs are in fact from magnetar flares. Most or all fast radio bursts could be magnetars?
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- Our Sun is only one of the billions of stars in our galaxy, the Milky Way. It’s also quite small compared to other stars, many are at least eight times more massive. These massive stars influence the structure, shape and chemical content of a galaxy.
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- When massive stars have exhausted their hydrogen gas fuel and die, they do so in an explosive event called a “supernova“. This explosion is sometimes so strong that it triggers the formation of new stars out of materials in the dead star’s surroundings.
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- But there’s an important gap in our knowledge: astronomers don’t yet fully understand how those original massive stars themselves are initially formed. So far, observations have only yielded some pieces of the puzzle. This is because nearly all the known massive stars in our galaxy are located very far away from our solar system.
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- Astronomers have recently found that the “funneling” of matter into a forming star happens at different rates over time. Sometimes the forming star swallows up a huge amount of matter, resulting in a burst of activities in the massive star. This is called an “accretion burst event“. It is incredibly rare: only three such events have been observed, out of all the billions of massive stars in the Milky Way.
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- After the first detection of an accretion burst, in 2016, astronomers from around the world agreed in 2017 to coordinate their efforts to observe more. Reported bursts have to be validated and followed up with more observations, and this takes a joint, global effort.
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- A “maser” is the microwave (radio frequency) equivalent of laser. The word stands for “microwave amplification by stimulated emission of radiation”. Masers are observed using radio telescopes and most of them are observed at centimeter wavelength.
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- A “maser flare” can be a sign of an extraordinary event such as the formation of a star. In January 2019, astronomers noticed that one such massive protostar, G358-MM1, showed signs of new activity. The masers associated with the object brightened significantly over a short period of time. The theory is that masers brighten when excited by an accretion burst.
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- Follow-up observations with the Australian Long Baseline Array revealed something astronomers are witnessing for the first time, a blast of heat-wave coming from the source and traveling through the surroundings of the forming big star. Blasts can last for about two weeks to a few months.
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- Blasts like this were not observed in the previous two accretion bursts in massive stars. This may imply that it’s a different kind of accretion burst. There may even be a “zoo” of accretion burst types – a whole range of different types which act in different ways that may depend on the mass and evolutionary stage of the young star.
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- Although the burst activity has died down, the masers are still a lot brighter than they were before the burst. Astronomers are watching with interest to see whether a similar burst will occur again, and at what scale.
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September 20, 2022 MAGNETARS and MASERS 3689
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