Astronomy Mysterious black hole flares at the center of the Milky Way
A star with a very peculiar chemical composition has been found.
It appears to be the result of a gigantic stellar explosion that took place shortly after the Big Bang.
Supernovae and hypernovae
At the end of its life, a massive star, with at least 10 times the mass of the Sun, depletes the nuclear fuel in its interior by successively burning hydrogen, helium and carbon, until it reaches iron.
From this moment on, the stellar interior is no longer capable of generating more nuclear energy, the system is completely destabilized and a large explosion is triggered.
This is what is known by the pretty term supernova.
When a star explodes as a supernova, its luminosity can increase up to 100,000 times.
This extremely intense brightness lasts for several days and, if the star is close enough, it is easily observed from Earth.
In the central region of the ejected material, the stellar corpse turns into a neutron star or pulsar.
If the mass of the dying star exceeds 25 solar masses, the explosion it produces is about ten times more luminous than a normal supernova and is known as a hypernova.
In this case, the final stellar residue will be a black hole.
During the explosion of a hypernova, very energetic jets of plasma are also generated that arise from the polar regions of the star and give rise to powerful gamma radiation.
Exceptional star
David Yong, from the ASTRO 3D center at the Australian National University, has coordinated a team of astronomers who have found a star with exceptional characteristics.
It is a red star, most likely the remnant of a hypernova explosion.
It is located about 7,500 light years away, in a peripheral region of the Milky Way and is observable in the constellation of the Eagle.
Its name in astronomical slang is SMSS J200322.54-114203.3, but let's leave it here at J200 for short.
The star J200 in the constellation of the Eagle SkyMapper / Da Costa
What makes this star exceptional is its chemical composition. In the first place, it stands out for its very low abundance in iron: its iron to hydrogen ratio is 3,000 times less than the value in the Sun. Second, it stands out for its high abundance of heavy metallic elements such as zinc, uranium, europium and even gold. . These abundances are much higher than in the Sun and than in many other evolved stars.
The usual known processes that make up these heavy elements (known as "r processes") occur in the collisions of two neutron stars.
To put it briefly, in these collisions the fast neutron capture mechanisms allow the atomic nuclei to get heavier and heavier, thus generating these metallic elements.
However, in the case of the star J200, such mechanisms would have been insufficient to explain its high metal abundances.
In the universe baby
Yong and colleagues conclude that the only explanation for J200's exotic chemical composition is that it was produced by the collapse of the core of a strongly magnetized massive star and rotating at high speeds.
In other words, it could have been created in the explosion, in the form of a hypernova, of a star with more than 25 solar masses.
Normally, as noted above, in a hypernova, the stellar corpse turns into a black hole.
However, in the case of J200, the very fast rotation and its intense magnetic field would have prevented, for the moment, the definitive collapse and would have created this stellar object in which all the stable elements of the periodic table have been produced.
Other hypernova explosions have been detected.
But what makes J200 very special is its age: it was formed 13 billion years ago, that is, when the age of the universe did not reach one billion years.
If we compare the current universe with an adult human being, the universe was then a baby.
It was an exciting time in cosmic history, the time when galaxies were still forming.
Studying these moments in the evolution of the universe can provide us with very valuable clues about how the cosmos came to be configured as we know it today.
Finding a hypernova like J200 in the Milky Way is an indication that this type of explosion could be relatively frequent at that time, which could contribute to precipitate the formation of more and more stars in the early universe.
For all these reasons, it is important to continue looking for stars similar to J200, extremely old and with a peculiar chemical composition. They are authentic cosmic time capsules, they provide us with very valuable information about the early evolution of our universe.
Yong's team identified the very iron-poor star J200 during a scan of the sky with a 1.3-meter-diameter telescope located in Australia (SkyMapper project).
The same team then made more detailed observations with the 2.3-meter telescope at the Siding Spring Observatory (Australia) and the 6.5-meter Large Magellan Telescope located in the Atacama Desert (Chile).
His work has been published a few days ago in the journal
Nature
.
The article entitled
r-Process elements from magnetorotational hypernovae
can be consulted at this link.
_________________________________________________________
Rafael Bachiller is director of
the National Astronomical Observatory
(National Geographic Institute) and academic of the
Royal Academy of Doctors of Spain.
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