The strange case of 2019yvr supernova In a recent study, a team of astronomers led
by Northwestern University describes the characteristics of a supernova that exploded in 2019 and its
progenitor star, a yellow supergiant, observed two and a half years apart. The results show
a discrepancy in the hydrogen content that leads to a re-evaluation of what is possible
during the end of life of the most massive stars.
Follow me in this video to get to know more about the explosive death of stars! You won't
regret it!
“When I had satisfied myself that no star of that kind had ever shone before, I was
led into such perplexity by the unbelievability of the thing that I began to doubt the faith
of my own eyes.”
This is a quote attributed to the Danish astronomer Tycho Brahe, that in 1572 was among those
who noticed a new bright object in the constellation Cassiopeia.
Adding fuel to the intellectual fire that Copernicus started, Tycho showed this “new
star” was far beyond the Moon, and that it was possible for the universe beyond the
Sun and planets to change. Astronomers now know that Tycho’s new star
was not new at all. Rather it signalled the death of a star in a supernova, an explosion
so bright that it can outshine the light from an entire galaxy. This particular supernova
was a Type Ia, which occurs when a white dwarf star pulls material from or merges with, a
nearby companion star until a violent explosion is triggered. The white dwarf star is obliterated,
sending its debris hurtling into space. In its two decades of operation, NASA’s Chandra
X-ray Observatory has captured unparalleled X-ray images of many supernova remnants, and of
course it took a look at Tycho. Chandra telescope revealed an intriguing pattern
of bright clumps and fainter areas in Tycho's Supernova.
Here you can see Tycho's supernova as seen by Chandra.
To emphasize the clumps in the image and the three-dimensional nature of Tycho, scientists
selected two narrow ranges of X-ray energies to isolate material (silicon, coloured red)
moving away from Earth, and moving towards us (also silicon, coloured blue). The other
colours in the image (yellow, green, blue-green, orange and purple) show a broad range of different
energies and elements and a mixture of directions of motion. In this new composite image, Chandra’s
X-ray data have been combined with an optical image of the stars in the same field of view
from the Digitized Sky Survey.
This was meant to be a little historical introduction to the important discovery we are going to
discuss. But we also need some detailed information
about the life cycle of a very large star, because eventually, it will end in a supernova.
As we all know, stars are formed in clouds of gas and dust, known as nebulae.
Nuclear reactions at the centre (or core) of stars provide enough energy to make them
shine brightly for many years, and this stage is known as the 'main sequence'.
Very large, massive stars burn their fuel much faster than smaller stars and may only
last a few hundred thousand years. When the hydrogen fuel that powers the nuclear reactions
within stars will begin to run out the star will enter the final phase of its lifetime.
Over time, it will expand, cool and change colour to become red giants. The path they
follow beyond that depends on the mass of the star.
Massive stars will experience a most energetic and violent end, which will see their remains
scattered about the cosmos in an enormous explosion, called a supernova. Once the dust
clears, the only thing remaining will be a very dense star known as a neutron star,
these can often be rapidly spinning and are known as pulsars. If the star which explodes
is especially large, it can even form a black hole.
So we learned that a supernova is probably the biggest explosion that humans have ever
seen. Each blast is the extremely bright, super-powerful explosion of a star.
These spectacular events can be so bright that they outshine their entire galaxies for
a few days or even months. They can be seen across the universe, that's why they are very
good as “candles”: astronomers use supernovae like rulers, to measure distances in space.
It is pretty difficult to observe a new supernova. Astronomers believe that about two or three
supernovas occur each century in galaxies like our own Milky Way. Because the universe
contains so many galaxies, astronomers observe a few hundred supernovas per year outside
our galaxy. Space dust blocks our view of most of the supernovas within the Milky Way.
Scientists have learned a lot about the universe by studying supernovas.
They learned that stars are the universe’s factories. Stars generate the chemical elements
needed to make everything in our universe. At their cores, stars convert simple elements
like hydrogen into heavier elements. These heavier elements, such as carbon and nitrogen,
are the elements needed for life. Only massive stars can make heavy elements
like gold, silver, and uranium. When explosive supernovas happen, stars distribute both stored-up
and newly-created elements throughout space. Now we are ready to understand the importance
of the new study by Northwestern University. Anyway, the supernovae only occasionally
reveal their past history. Sometimes, however, archival images of the galaxy in which the
explosion occurred can help uncover what the star looked like before its last sign. And
when that happens, as happened to a team of astronomers led by Northwestern University
(USA), the result can be unexpected. For example, it may happen that in the supernova spectrum
the signature of hydrogen is detected, but that there is no trace of it in its progenitor
star.
This is the case of the supernova 2019yvr and its candidate parent star, a yellow supergiant,
observed two and a half years apart by Charles Kilpatrick, a researcher at the Center for
Interdisciplinary Exploration and Research in Astrophysics of Northwestern University,
and his colleagues. Sn 2019yvr is a supernova discovered inside
the spiral galaxy Ngc 4666 on December 27, 2019, by the telescopes of the Atlas program
( Asteroid terrestrial impact last alert system ). The supernova was observed with
the help of some telescopes located in Chile, and the analysis of the light curves and spectra
showed that it is of a type Ib supernova: an explosion, produced by the full-blown death
of stars with a mass of at least nine times that of the Sun, in which the ejected material
is devoid of hydrogen. Scientists asked themselves which was the
progenitor of that supernova who caused the big explosion?
"What massive stars do just before they explode is a great unsolved mystery," says
Kilpatrick. "It is rare to see this type of star before it explodes in a supernova."
However, astronomers didn't give up and guess what they did?
They managed to recover images of deep space previously captured by the fantastic NASA's
Hubble Space Telescope - which had observed the same section of the sky where Sn 2019yvr
was spotted two and a half years before the star exploded - in search of the progenitor
star of the "cosmic bang". The Hubble images have made it possible to
identify as a progenitor candidate a yellow supergiant of about 30 solar masses located
35 million light-years from Earth in the Virgo cluster of galaxies. A star, the researchers
explain, whose relatively cold surface temperature - 6,500 degrees Celsius - implies a huge envelope
of hydrogen, but there is no trace of it in its supernova. In short, the identified star
has very different characteristics from those typical of type I supernova progenitors, which
are believed to have compact and low-mass envelopes, consistent with a star almost devoid
of hydrogen in its outer layers.
In this pic, you can see the Hubble Space Telescope (HST) imaging showing the explosion
site of 2019yvr from 2.5 years before its explosion. On the upper left: the supernova
itself is seen in an image from the Gemini-South telescope 72 days after it exploded. On the
lower left: a zoom in to the same site in the pre-explosion HST image, showing a single
source that appears to be the progenitor star of 2019yvr.
Astronomers have never seen such a thing. In fact, if a star explodes without hydrogen,
it should be a blue star, so very hot indeed. It is almost impossible for a star to be this
cold without having hydrogen in its outer layers. << We looked at every single stellar
pattern that could explain a star like this, and each predicted it to have hydrogen - which,
from its supernova, we know it did not. A fact that leads to expanding what is physically
possible ». said, Kilpatrick. How then to explain this apparent contradiction?
How to explain the observation of a supernova without a significant mass of hydrogen and
a progenitor star whose characteristics are consistent with a massive star that generally
has a non-negligible mass of hydrogen in its outer layers?
Here comes the potential of this discovery! In fact, several months after the supernova
explosion, scientists have some clues: they suppose the material ejected from the supernova
could have collided with a large mass of hydrogen. This led the researchers to speculate that
the parent star may have ejected the hydrogen from its outer layers many years before exploding.
The discovery of this star provides some of the most direct evidence ever found that stars
suffer such mass losses. If the star underwent these eruptions, it probably ejected its hydrogen
several decades before it exploded. But in the study, Kilpatrick's team also presents
another possibility, which is that a less massive companion star may have been stripping
the hydrogen away from the supernova's progenitor star. The team, however, won't be able to
test this hypothesis until the supernova's brightness dims, which could take up to a
decade.
What else could we say? We just have to wait and keep loving science!
"What do you think about this new exciting discovery? Does it amaze you? Let us know
in the comment below! If you would like to help improve the quality of our content, please
check us out on patreon, we would like to say a big thank you to all those who show
their support.”