- 4130 - MAGNETARS - the death of massive stars? At least 29 known magnetars exist in the Milky Way Galaxy, visible to us through their X-ray and gamma-ray emissions. Eventually, the magnetic fields relax and fade and the emissions stop. That leaves behind a dead core. It’s likely that our galaxy has tens of millions of inactive magnetars.
-------------- 4130 - MAGNETARS - the death of massive stars?
- The Earth is a magnet with a north and
south poles. Could stars be magnets?
Imagine a living star with a magnetic field at least 100,000 times stronger
than Earth’s field. That’s the strange stellar “ HD 45166”.
-
- Its field is an incredible 43,000 Gauss.
That makes it a new type of object: a “massive magnetic helium star”. In a
million years, it’s going to get even stranger when it collapses and becomes a
type of neutron star called a “magnetar”.
-
- HD 45166 provides clues to the creation of
magnetars. This object is no ordinary
massive star. It is what’s left after the merger of two lower-mass helium
stars. The result is this heavily
magnetized helium star which mimics the core of a star that was originally 8
times more massive than our Sun. It is
massive enough to explode as a supernova and collapse into a neutron star.
-
- It is
a highly unusual star that is destined to become one of the most magnetic
objects in the Universe: a variant of a neutron star known as a magnetar. This
finding marks the discovery of a new type of astronomical object, a massive
magnetic helium star and sheds light on the origin of magnetars.
-
- Eventually, HD 45166 will explode as a very
bright, but not particularly energetic, supernova. Its core will contract,
trapping and concentrating the star’s magnetic field lines. The result will be
a neutron star with a magnetic field that is far greater.
-
- The newly formed helium object is a highly
evolved “Wolf-Rayet star”. Before it becomes a magnetar, it has to go through
some more changes. Stellar evolution models suggest that it will eventually explode
as a type Ib or IIb supernova.
-
- As it collapses under its own gravity, the
already-strong magnetic field will grow. Eventually, the object will become a
very compact core with a magnetic field of around 100 trillion Gauss. That
would make it one of the most powerful types of magnet in the Universe: a
magnetar.
-
- HD 45166 is actually a stellar pair, of
which the “Wolf-Rayet star” is one member. Astronomers have observed it for
more than a century, but its strange characteristics defied explanation.
-
- In February 2022 the team used an
instrument on the Canada-France-Hawaii Telescope that can detect and measure
magnetic fields. They also relied on archival data taken with the “Fiber-fed
Extended Range Optical Spectrograph” (FEROS) at ESO’s La Silla Observatory in
Chile. That’s how the team found out the star had a magnetic field strength of
43 kiloGauss.
-
- The entire surface of the helium star has a
magnetic field almost 100,000 times stronger than Earth’s. This observation marks the discovery of the
very first massive magnetic helium star.
-
- How Do Magnetars Form? Magnetaes neutron stars, the hot leftovers
from the deaths of supermassive stars. Essentially, neutron stars are the cores
of the once-living supermassive stars. They’re no longer stars with nuclear
fusion going on in their cores. Instead, these beasts are spinning spheres of
condensed neutrons packed together incredibly tightly. All that mass has very
strong gravity. Something inside is
generating a magnetic field that is trillions of times stronger than Earth’s.
-
- Magnetars generate magnetic fields a
thousand times stronger than their progenitor neutron stars. The process comes
from a magnetohydrodynamic process in conducting “fluids” inside the star. This
is roughly similar to what happens in the turbulent center of our planet. Like
their neutron star predecessors, magnetars likely have solid, crusty surfaces.
-
- Astronomers continue to probe these objects
for clues to the origins of their magnetic fields. As far back as 2009, they
entertained the idea that stellar mergers could create conditions for such
strong fields. The origin of the
magnetic field in HD 45166 probably goes back to the process that created the
proto-magnetar. It gave rise to the hefty magnetic field that got “frozen” into
the layers of the star. That field will be the future magnetar.
-
-
August 28, 2023 MAGNETARS
- the death of massive
stars? 4130
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Monday, August 28, 2023 ---------------------------------
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