In an ejection that would have caused its rotation to slow, a magnetar is depicted losing material into space in this artist’s concept. The magnetar’s strong, twisted magnetic field lines (shown in green) can influence the flow of electrically charged material from the object, which is a type of neutron star. NASA/JPL-Caltech
Using two of the agency’s X-ray telescopes, researchers were able to zoom
in on a dead star’s erratic behavior as it released a bright, brief burst of
radio waves.
What’s causing mysterious bursts
of radio waves from deep space? Astronomers may be a step closer to providing one
answer to that question. Two NASA X-ray telescopes recently observed one such
event – known as a fast radio burst – mere minutes before and after it
occurred. This unprecedented view sets scientists on a path to better
understand these extreme radio events.
While they only last for a fraction
of a second, fast radio bursts can release about as much energy as the Sun does
in a year. Their light also forms a laserlike beam, setting them apart from
more chaotic cosmic explosions.
Because the bursts are so brief,
it’s often hard to pinpoint where they come from. Prior to 2020, those that
were traced to their source originated outside our own galaxy – too far away
for astronomers to see what created them. Then a fast radio burst erupted in Earth’s home galaxy, originating from an extremely dense object called a
magnetar – the collapsed remains of an exploded star.
In October 2022, the same magnetar
– called SGR 1935+2154 – produced another fast radio burst, this one studied in
detail by NASA’s NICER (Neutron Star Interior Composition Explorer) on
the International Space Station and NuSTAR (Nuclear Spectroscopic Telescope Array) in low Earth orbit. The
telescopes observed the magnetar for hours, catching a glimpse of what happened
on the surface of the source object and in its immediate surroundings, before
and after the fast radio burst. The results, described in a new study published Feb. 14 in the journal Nature, are an example of how NASA
telescopes can work together to observe and follow up on short-lived events in the cosmos.
The burst occurred between two
“glitches,” when the magnetar suddenly started spinning faster. SGR 1935+2154
is estimated to be about 12 miles (20 kilometers) across and spinning about 3.2
times per second, meaning its surface was moving at about 7,000 mph (11,000
kph). Slowing it down or speeding it up would require a significant amount of
energy. That’s why study authors were surprised to see that in between
glitches, the magnetar slowed down to less than its pre-glitch speed in just
nine hours, or about 100 times more rapidly than has ever been observed in a
magnetar.
“Typically, when glitches happen,
it takes the magnetar weeks or months to get back to its normal speed,” said
Chin-Ping Hu, an astrophysicist at National Changhua University of Education in
Taiwan and the lead author of the new study. “So clearly things are happening
with these objects on much shorter time scales than we previously thought, and
that might be related to how fast radio bursts are generated.”
Spin Cycle
When trying to piece together
exactly how magnetars produce fast radio bursts, scientists have a lot of variables to consider.
For example, magnetars (which are a
type of neutron star) are so dense that a teaspoon of their material would weigh about a billion tons on Earth. Such a high density also means a strong
gravitational pull: A marshmallow falling onto a typical neutron star would
impact with the force of an early atomic bomb.
The strong gravity means the
surface of a magnetar is a volatile place, regularly releasing bursts of X-rays and higher-energy light. Before the fast radio burst
that occurred in 2022, the magnetar started releasing eruptions of X-rays and
gamma rays (even more energetic wavelengths of light) that were observed in the
peripheral vision of high-energy space telescopes. This increase in activity
prompted mission operators to point NICER and NuSTAR directly at the magnetar.
“All those X-ray bursts that
happened before this glitch would have had, in principle, enough energy to
create a fast radio burst, but they didn’t,” said study co-author Zorawar
Wadiasingh, a research scientist at the University of Maryland, College Park
and NASA’s Goddard Space Flight Center. “So it seems like something changed during the
slowdown period, creating the right set of conditions.”
What else might have happened with
SGR 1935+2154 to produce a fast radio burst? One factor might be that the
exterior of a magnetar is solid, and the high density crushes the interior into
a state called a superfluid. Occasionally, the two can get out of sync, like
water sloshing around inside a spinning fishbowl. When this happens, the fluid
can deliver energy to the crust. The paper authors think this is likely what
caused both glitches that bookended the fast radio burst.
If the initial glitch caused a
crack in the magnetar’s surface, it might have released material from the
star’s interior into space like a volcanic eruption. Losing mass causes
spinning objects to slow down, so the researchers think this could explain the
magnetar’s rapid deceleration.
But having observed only one of
these events in real time, the team still can’t say for sure which of these
factors (or others, such as the magnetar’s powerful magnetic field) might lead
to the production of a fast radio burst. Some might not be connected to the
burst at all.
“We’ve unquestionably observed
something important for our understanding of fast radio bursts,” said George
Younes, a researcher at Goddard and a member of the NICER science team
specializing in magnetars. “But I think we still need a lot more data to complete
the mystery.”
More About the
Mission
A Small Explorer mission led by
Caltech and managed by NASA’s Jet Propulsion Laboratory in Southern California
for the agency’s Science Mission Directorate in Washington, NuSTAR was
developed in partnership with the Danish Technical University and the Italian
Space Agency (ASI). The spacecraft was built by Orbital Sciences Corp. in
Dulles, Virginia. NuSTAR’s mission operations center is at the University of
California, Berkeley, and the official data archive is at NASA’s High Energy
Astrophysics Science Archive Research Center at NASA’s Goddard Space Flight
Center. ASI provides the mission’s ground station and a mirror data archive.
Caltech manages JPL for NASA.
For more information about the
NuSTAR mission, visit:
https://www.nustar.caltech.edu/
NICER, an Astrophysics Explorer
Mission of Opportunity, is an external payload on the International Space
Station. NICER is managed by and operated at NASA’s Goddard Space Flight
Center; its data is archived at NASA’s HEASARC. NASA’s Explorers program provides
frequent flight opportunities for world-class scientific investigations from
space utilizing innovative, streamlined, and efficient management approaches
within the heliophysics and astrophysics science areas.
For more information about the
NICER mission, visit:
Source: NASA Telescopes Find New Clues About Mysterious Deep Space Signals - NASA
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