Cosmic flashes pinpointed to a surprising location in space

Date:
February 23, 2022
Source:
Chalmers University of Technology
Summary:
Astronomers have been surprised by the closest source of mysterious
flashes in the sky called fast radio bursts. Precision measurements
with radio telescopes reveal that the bursts are made among old
stars, and in a way that no one was expecting. The source of the
flashes, in nearby spiral galaxy M 81, is the closest of its kind
to Earth.



FULL STORY ========================================================================== Astronomers have been surprised by the closest source of mysterious
flashes in the sky called fast radio bursts. Precision measurements
with radio telescopes reveal that the bursts are made among old stars,
and in a way that no one was expecting. The source of the flashes,
in nearby spiral galaxy M 81, is the closest of its kind to Earth.


==========================================================================
Fast radio bursts are unpredictable, extremely short flashes of light
from space. Astronomers have struggled to understand them ever since
they were first discovered in 2007. So far, they have only ever been
seen by radio telescopes.

Each flash lasts only thousandths of a second. Yet each one sends out
as much energy as the Sun gives out in a day. Several hundred flashes
go off every day, and they have been seen all over the sky. Most lie at
huge distances from Earth, in galaxies billions of light years away.

In two papers published in parallel this week in the journals Nature
andNature Astronomy, an international team of astronomers present
observations that take scientists a step closer to solving the mystery --
while also raising new puzzles. The team is led jointly by Franz Kirsten (Chalmers, Sweden, and ASTRON, Netherlands) and Kenzie Nimmo (ASTRON
and University of Amsterdam).

The scientists set out to make high-precision measurements of a repeating
burst source discovered in January 2020 in the constellation of Ursa
Major, the Great Bear.

"We wanted to look for clues to the bursts' origins. Using many radio telescopes together, we knew we could pinpoint the source's location in
the sky with extreme precision. That gives the opportunity to see what the local neighbourhood of a fast radio burst looks like," says Franz Kirsten.



==========================================================================
To study the source at the highest possible resolution and sensitivity,
the scientists combined measurements from telescopes in the European VLBI Network (EVN). By combining data from 12 dish antennas spread across half
the globe, Sweden, Latvia, The Netherlands, Russia, Germany, Poland,
Italy and China, they were able to find out exactly where in the sky
they were coming from.

The EVN measurements were complemented with data from several other
telescopes, among them the Karl G. Jansky Very Large Array (VLA) in New
Mexico, USA.

Close but surprising location When they analysed their measurements, the astronomers discovered that the repeated radio flashes were coming from somewhere no one had expected. They traced the bursts to the outskirts
of the nearby spiral galaxy Messier 81 (M 81), about 12 million light
years away. That makes this the closest ever detection of a source of
fast radio bursts.

There was another surprise in store. The location matched exactly with
a dense cluster of very old stars, known as a globular cluster.



========================================================================== "It's amazing to find fast radio bursts from a globular cluster. This
is a place in space where you only find old stars. Further out in the
universe, fast radio bursts have been found in places where stars are
much younger. This had to be something else," says Kenzie Nimmo.

Many fast radio bursts have been found surrounded by young, massive
stars, much bigger than the Sun. In those locations, star explosions
are common and leave behind highly magnetised remnants.Scientists have
come to believe that fast radio bursts can be created in objects known
as magnetars. Magnetars are the extremely dense remnants of stars that
have exploded. And they are the universe's most powerful known magnets.

"We expect magnetars to be shiny and new, and definitely not surrounded
by old stars. So if what we're looking at here really is a magnetar,
then it can't have been formed from a young star exploding. There has to
be another way," says team member Jason Hessels, University of Amsterdam
and ASTRON.

The scientists believe that the source of the radio flashes is something
that has been predicted, but never seen before: a magnetar that formed
when a white dwarf became massive enough to collapse under its own weight.

"Strange things happen in the multi-billion-year life of a tight cluster
of stars. Here we think we're seeing a star with an unusual story,"
explains Franz Kirsten.

Given time, ordinary stars like the Sun grow old and transform into
small, dense, bright objects called white dwarfs. Many stars in the
cluster live together in binary systems. Of the tens of thousands of
stars in the cluster, a few get close enough that one star collects
material from the other.

That can lead to a scenario known as "accretion-induced collapse,"
Kirsten explains.

"If one of the white dwarfs can catch enough extra mass from its
companion, it can turn into an even denser star, known as a neutron
star. That's a rare occurrence, but in a cluster of ancient stars, it's
the simplest way of making fast radio bursts," says team member Mohit
Bhardwaj, McGill University, Canada.

Fastest ever Looking for further clues by zooming into their data,
the astronomers found another surprise. Some of the flashes were even
shorter than they had expected.

"The flashes flickered in brightness within as little as a few tens of nanoseconds. That tells us that they must be coming from a tiny volume
in space, smaller than a soccer pitch and perhaps only tens of metres
across," says Kenzie Nimmo.

Similarly lightning-fast signals have been seen from one of the sky's
most famous objects, the Crab pulsar. It is a tiny, dense, remnant
of a supernova explosion that was seen from Earth in 1054 CE in the constellation of Taurus, the Bull. Both magnetars and pulsars are
different kinds of neutron stars: super-dense objects with the mass of
the Sun in a volume the size of a city, and with strong magnetic fields.

"Some of the signals we measured are short and extremely powerful, in
just the same way as some signals from the Crab pulsar. That suggests
that we are indeed seeing a magnetar, but in a place that magnetars
haven't been found before," says Kenzie Nimmo.

Future observations of this system and others will help to tell whether
the source really is an unusual magnetar, or something else, like an
unusual pulsar or a black hole and a dense star in a close orbit.

"These fast radio bursts seem to be giving us new and unexpected insight
into how stars live and die. If that's true, they could, like supernovae,
have things to tell us about stars and their lives across the whole
universe," says Franz Kirsten.

========================================================================== Story Source: Materials provided by
Chalmers_University_of_Technology. Note: Content may be edited for style
and length.


========================================================================== Journal References:
1. F. Kirsten, B. Marcote, K. Nimmo, J. W. T. Hessels, M. Bhardwaj,
S. P.

Tendulkar, A. Keimpema, J. Yang, M. P. Snelders, P. Scholz, A. B.

Pearlman, C. J. Law, W. M. Peters, M. Giroletti, Z. Paragi,
C. Bassa, D.

M. Hewitt, U. Bach, V. Bezrukovs, M. Burgay, S. T. Buttaccio, J. E.

Conway, A. Corongiu, R. Feiler, O. Forsse'n, M. P. Gawroński,
R.

Karuppusamy, M. A. Kharinov, M. Lindqvist, G. Maccaferri,
A. Melnikov, O.

S. Ould-Boukattine, A. Possenti, G. Surcis, N. Wang, J. Yuan, K.

Aggarwal, R. Anna-Thomas, G. C. Bower, R. Blaauw, S. Burke-Spolaor,
T.

Cassanelli, T. E. Clarke, E. Fonseca, B. M. Gaensler, A. Gopinath,
V. M.

Kaspi, N. Kassim, T. J. W. Lazio, C. Leung, D. Z. Li, H. H. Lin,
K. W.

Masui, R. Mckinven, D. Michilli, A. G. Mikhailov, C. Ng,
A. Orbidans, U.

L. Pen, E. Petroff, M. Rahman, S. M. Ransom, K. Shin, K. M. Smith,
I. H.

Stairs, W. Vlemmings. A repeating fast radio burst source
in a globular cluster. Nature, 2022; 602 (7898): 585 DOI:
10.1038/s41586-021-04354-w
2. K. Nimmo, J. W. T. Hessels, F. Kirsten, A. Keimpema, J. M. Cordes,
M. P.

Snelders, D. M. Hewitt, R. Karuppusamy, A. M. Archibald,
V. Bezrukovs, M.

Bhardwaj, R. Blaauw, S. T. Buttaccio, T. Cassanelli, J. E. Conway,
A.

Corongiu, R. Feiler, E. Fonseca, O. Forsse'n, M. Gawroński, M.

Giroletti, M. A. Kharinov, C. Leung, M. Lindqvist, G. Maccaferri, B.

Marcote, K. W. Masui, R. Mckinven, A. Melnikov, D. Michilli, A. G.

Mikhailov, C. Ng, A. Orbidans, O. S. Ould-Boukattine, Z. Paragi,
A. B.

Pearlman, E. Petroff, M. Rahman, P. Scholz, K. Shin, K. M. Smith,
I. H.

Stairs, G. Surcis, S. P. Tendulkar, W. Vlemmings, N. Wang, J. Yang,
J. P.

Yuan. Burst timescales and luminosities as links between young
pulsars and fast radio bursts. Nature Astronomy, 2022; DOI:
10.1038/s41550-021- 01569-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220223133512.htm

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