Artist's impression of magnetar. Credit: ESO/L. Calçada
Magnetars are the super-dense leftovers
of supernova detonations. Magnetars are the strongest magnets so far identified
in the Universe. Magnetars are actually millions of times more powerful than any
of the strongest magnets on the Planet Earth. Recently a team of astrophysicists
using ESO's Very Large Telescope now consider that they've discovered the companion
star of a magnetar for the first time. This recent finding helps to clarify how
magnetars form and why this specific star didn't collapse into a black hole as astrophysicists
would assume.
The Westerlund 1 star cluster
is positioned 16 000 light-years away in the southern constellation of Ara and contains
one of the two dozen magnetars so far discovered in the Milky Way Galaxy. It is
entitled as CXOU J164710.2-455216 and it has seriously confused astronomers.
When a massive star collapses due
to its own gravity through a supernova detonation it forms one or the other a
black hole or a neutron star and Magnetars are rare and very unusual kind of
neutron star. Like neutron stars they are tiny and extremely dense but they
also produce enormously powerful magnetic fields. Magnetar surfaces also
release huge quantities of gamma rays.
Astrophysicists suggested an explanation
to this mystery. They proposed that the magnetar made by the connections of two
very gigantic stars circling one another in a binary system so dense that it
would fit inside the orbit of the Earth around the Sun. But, until now, no partner
star was discovered at the position of the magnetar in Westerlund 1, so astrophysicists
used the VLT to hunt for it in other regions of the cluster. They searched for escaped
stars (objects dodging the cluster at high velocities) that might have been hit
out out of orbit by the supernova detonation that made the magnetar. One star, identified
as Westerlund 1-5, was discovered to be doing just that.
Ben Ritchie (Open University),
a co-author on the new paper says “Not only does this star have the high
velocity expected if it is recoiling from a supernova explosion, but the
combination of its low mass, high luminosity and carbon-rich composition appear
impossible to replicate in a single star—a smoking gun that shows it must have
originally formed with a binary companion,”
This finding allowed the stargazers
to rebuild the stellar life story that allowed the magnetar to form, instead of
the predicted black hole. In the initial phase of this procedure, the more
massive star of the pair initiates to run out of its fuel, relocating its external
layers to its less massive partner star, which is meant to turn into the
magnetar, initiating it to revolve more and more rapidly. This rapid spin seems
to be the vital component in the creation of the magnetar's ultra-strong
magnetic field.
In the next phase, as an outcome
of this mass transmission, the partner itself becomes so gigantic that it in
turn sheds a huge amount of its newly extended mass. Considerable amount of
this mass is lost but some is handed back to the original star that we still see
shining currently as Westerlund 1-5. It appears that being a partner of a binary
star might therefore be a vital component in the procedure for making a magnetar.
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