Probing the magnetar at the center of our galaxy

Orange sphere with golden shoots.
Illustration of a magnetar — a rotating neutron star with incredibly powerful magnetic fields. Image via NASA/CXC/M.Weiss.

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A team of scientists have analyzed pulses of radio waves coming from a magnetar – a rotating, dense, dead star with a strong magnetic field – that is located near the supermassive black hole at the heart of the Milky Way galaxy. The new research provides clues that magnetars like this one, lying in close proximity to a black hole, could perhaps be linked to the source of fast radio bursts, or FRBs. FRBs are high-energy blasts that originate beyond our galaxy but whose exact nature is unknown.

Caltech graduate student Aaron Pearlman presented the results yesterday (January 9, 2019) at the meeting of the American Astronomical Society in Seattle. He said in a statement:

Our observations show that a radio magnetar can emit pulses with many of the same characteristics as those seen in some FRBs. Other astronomers have also proposed that magnetars near black holes could be behind FRBs, but more research is needed to confirm these suspicions.

Magnetars are a rare subtype of a group of objects called pulsars. Pulsars, in turn, belong to a class of rotating dead stars known as neutron stars. Magnetars are thought to be young pulsars that spin more slowly than ordinary pulsars and have much stronger magnetic fields, which suggests that perhaps all pulsars go through a magnetar-like phase in their lifetime.

This video from NASA, released in May 2018, explores the idea that radio pulsars and magnetars might be 2 sides of the same coin, that is, 2 stages in the life of a single object.

The research, published October 24, 2018, in the peer-reviewed Astrophysical Journal, looked at the magnetar named PSR J1745-2900, which is located in the Milky Way’s galactic center, using the largest of NASA’s Deep Space Network radio dishes in Australia. PSR J1745-2900 is the closest known pulsar to the supermassive black hole at the center of the galaxy, separated by a distance of only 0.3 light-years, and it is the only pulsar known to be gravitationally bound to the black hole and the environment around it.

In addition to discovering similarities between the galactic-center magnetar and FRBs, the researchers also gleaned new details about the magnetar’s radio pulses. Using one of the Deep Space Network’s largest radio antennas, the scientists were able to analyze individual pulses emitted by the star every time it rotated, a feat that is very rare in radio studies of pulsars. They found that some pulses were stretched, or broadened, by a larger amount than predicted when compared to previous measurements of the magnetar’s average pulse behavior. Moreover, this behavior varied from pulse to pulse. Pearlman said:

We are seeing these changes in the individual components of each pulse on a very fast time scale. This behavior is very unusual for a magnetar.

The radio components, he noted, are separated by only 30 milliseconds on average.

One theory to explain the signal variability involves clumps of plasma moving at high speeds near the magnetar. Other scientists have proposed that such clumps might exist but, in the new study, the researchers propose that the movement of these clumps may be a possible cause of the observed signal variability. Another theory proposes that the variability is intrinsic to the magnetar itself.

Pearlman and his colleagues hope to use the Deep Space Network radio dish to solve another outstanding pulsar mystery: Why are there so few pulsars near the galactic center? Their goal is to find a non-magnetar pulsar near the galactic-center black hole. Pearlman said:

Finding a stable pulsar in a close, gravitationally bound orbit with the supermassive black hole at the galactic center could prove to be the Holy Grail for testing theories of gravity. If we find one, we can do all sorts of new, unprecedented tests of Albert Einstein’s general theory of relativity.

Bottom line: In a new study, researchers analyzed pulses of radio waves from a magnetar near the Milky Way galaxy’s central black hole.

Source: Pulse Morphology of the Galactic Center Magnetar PSR J1745-2900

Via Caltech

January 10, 2019

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