The universe’s most extreme stars just got a little more unexpected and mysterious.
Scientists were astonished to witness a “dead” neutron star with one of the strongest magnetic fields in the universe unexpectedly come to life. The reactivation of this highly magnetic neutron star, or “magnet,” does not fit with the current understanding of these exotic celestial bodies.
The team discovered this magnetar’s return from the dead when they used Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO) to detect strange radio signals coming from XTE J1810-197, the closest known magnetar to Earth, located approximately 8,000 light-years away. ) Parkes radio telescope, Murriyang.
Most magnetars are known to emit polarized light with waves directed in a specific direction. The team’s findings show that the light from this magnetar is circularly polarized and appears to spiral as it moves through space. This is not only unexpected, but also unprecedented.
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“Unlike the radio signals we’ve seen from other magnetars, this magnetar emits an enormous amount of rapidly changing circular polarization,” team leader and CSIRO scientist Marcus Lower said in a statement. “We’ve never seen anything like this before.”
The XTE J1810-197 is outstanding even for a magnetar
“We’ve never seen anything like this before.”
Like all neutron stars, magnetars are born when massive stars die. When these stars consume their fuel for the nuclear fusion of hydrogen into helium in their cores, the energy supporting them against the inward push of their own gravity is cut off.
Millions of years later, as the tug of war between gravity and radiation pressure comes to an end, the star’s outer layers are blown outward in a supernova explosion, causing the dying star to lose the vast majority of its mass.
This leaves a stellar core with a mass between one and two times the mass of the sun and collapses to a width of about 12 miles (20 kilometers), the size of an average city on Earth. As a result, the matter that makes up the neutron star is so dense that even a teaspoon brought to Earth would weigh 10 million tons.
Rapid core collapse also causes the neutron star to greatly increase its rotation rate; just like an ice skater pulling her arms to increase her spin, but on a much larger scale. This means that some newly formed neutron stars can spin as fast as 700 times per second.
There is another consequence of the collapse of this stellar core. The dying star’s magnetic field lines compress together, causing the strength of the magnetic field to increase. As a result, some neutron stars have magnetic fields quadrillions (1 followed by 15 zeros) times stronger than the sun’s magnetic field. This qualifies neutron stars into their own category, magnetars.
Detection of radio wave pulses from magnetars is incredibly rare; The XTE J1810-197 is one of only a handful of magnetars known to produce these. XTE J1810-197 was first seen emitting radio waves in 2003, but then this magnetar remained silent for more than a decade.
The magnetar was seen emitting radio waves again in 2018 by the 76-meter Lovell telescope at the University of Manchester’s Jodrell Bank Observatory. This was followed by Murriyang in Australia’s Wiradjuri Nation, who has observed XTE J1810-197 ever since.
Although this observation was completely unexpected, the team has an idea as to why this magnetar is producing such unusual emissions.
“Our results show that a superheated plasma exists above the magnetar’s magnetic pole, acting like a polarizing filter,” Lower said. “Exactly how the plasma does this is still to be determined.”
The 64-metre Murriyang telescope is equipped with a state-of-the-art ultra-wide bandwidth receiver designed by CSIRO engineers that is highly sensitive to brightness and polarization changes over a wide range of radio frequencies. This helps collect precise measurements of various celestial objects, especially magnetars.
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Researchers hope that continued observations of XTE J1810-197 with Murriyang will help provide information about a range of extreme, powerful and unusual phenomena associated with the magnetar, such as plasma dynamics, X-ray and gamma ray bursts, and potentially fast motions. radio bursts.
The team’s research was published in the journal Nature Astronomy.