Astronomers have discovered a new class of stellar object that appears to defy death in an unexplained way.
The object, located about 15,000 light years from Earth, appears to be a magnetar — the collapsed heart of a giant star, now cramming the sun’s worth of mass into a sphere no wider than a city, while crackling with a force field more than a quadrillion times stronger than Earth’s.
These tiny, swirling balls can emit a very bright beam of electromagnetic radiation as they spin, including radio waves that pulse into a steady, mysterious rhythm that usually repeats every few seconds or minutes. These radio pulses usually stop completely after a few months or years, as the magnetar’s rotation slows to a point called the “death line” — a theoretical threshold beyond which the star’s magnetic field becomes too weak to produce more high-energy radiation.
The newly discovered magnetar, however, appears to still be ablaze with bright, steady radiation from beyond the line of death – and has been for more than 30 years.
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“The object we found was rotating too slowly to generate radio waves – well below the death line,” Natasha Hurley-Walker, a radio astronomer at the Australian Center for International Radio Astronomy Research (ICRAR) and lead author of a new study on the object, said in a statement. “Assuming it is a magnetar, it should be impossible for this object to generate radio waves. But we saw it.”
If confirmed, these ultralong period magnetars could represent a new class of stellar objects that defies all current theoretical models.
Flashes beyond death
The magnetar was discovered by the Murchison Widefield Array radio telescope in Australia, with half a dozen other facilities around the world joining forces to confirm the discovery and study the mysterious object. (Image credit: ICRAR)
Scientists first discovered the highly persistent magnetar — dubbed GPM J1839−10 — in September 2022, using the Murchison Widefield Array, an array of radio telescopes in outback Australia. Their observations showed that the object pulsed with bright radio waves every 22 minutes, shining intensely for roughly five minutes before dimming again.
This is already a great observation; because most radio-emitting magnetars pulse every few seconds or minutes, this object’s 22-minute cycle makes it the longest-period magnetar ever found. The ultra-long cycle also means that the magnetar is rotating very slowly – beyond the death line.
To learn more about the unexplained object, the researchers compared magnetar observations from half a dozen other radio telescopes around the world, as well as examining archival data dating back to 1988. To the team’s surprise, they saw the same object appear in the oldest data set, pulsing at nearly the exact same 22-minute intervals, virtually unchanged for the past 33 years.
These strange qualities – the object’s slow rotation, extremely long pulse periods, and the extreme longevity of its radio emission regime – defy everything models have imposed on it, the researchers wrote. It’s possible that the object isn’t a magnetar at all. It could be a white dwarf – another type of stellar remnant – which is much larger than a magnetar and rotates more slowly. However, the team added, this object’s radio emission is at least 1,000 times brighter than the brightest white dwarf ever detected.
The problem is far from being solved.
“This extraordinary object challenges our understanding of neutron stars and magnetars, which are some of the most exotic and extreme objects in the universe,” said Hurley-Walker. “Whatever mechanism is behind this is amazing.”
The team’s research is published July 19 in the journal Nature.
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2023-07-24 02:19:40
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