Hello Space Fans and welcome to another edition of Space Fan News.
In this episode, astronomers observe a star that has gone supernova, not once, but twice;
the Giant Magellan Telescope starts casting its fifth mirror segment; and ALMA provides
us with the most detailed image of a red giant star ever produced and gives us a glimpse
of the fate of our own solar system.
Most space fans have learned by now, as most of us have been taught, that when very massive
stars die, they usually explode in a fiery event known as a supernova.
These cataclysmic deaths usually result in a beautiful, expanding cloud of stellar debris
that leaves behind a remnant: a rapidly spinning neutron star called a pulsar, or a black hole.
And, that’s usually it.
While this event is spectacular and amazing, it usually only happens once.
I mean, how many times can a star die, right?
Well, as with most things about the universe, things aren’t quite that simple.
Astronomers using the Keck Observatory on Mauna Kea in Hawai’i have found evidence
of a star that has gone supernova at least twice over the course of the last fifty years.
The Keck team was quite surprised and after having discovered some 5,000 supernovae, had
never seen one quite like this.
The spectra from this event looked like a ‘normal’ hydrogen-rich, core collapse
supernovae which last about 100 days, but the spectra from this one grew brighter and
dimmer at least five times more slowly, stretching out an event which normally lasts 100 days
to over two years.
The supernova, named iPTF14hls, was discovered in September of 2014 by the Palomar Transient
Factory (I love that name).
At the time, it looked like an ordinary supernova.
Several months later, Las Cumbres Observatory astronomers noticed the supernova was growing
brighter again after it had faded.
Well, that’s not normal, they must have said.
When astronomers went back and looked at archival data, they were surprised to find evidence
of an explosion in 1954 at the same location.
This star somehow survived that explosion and exploded again in 2014.
The star that blew up was at least 50 times more massive than the sun and probably much
larger.
Supernova iPTF14hls may have been the most massive stellar explosion ever seen.
The size of this explosion could be the reason that our conventional understanding of the
death of stars failed to explain this event.
So to try and understand this strange observation, astronomers did what scientists often do when
they see a new thing, they make up a new category of thing and put whatever it is in there.
What this might be, astronomers say, is a “Pulsational Pair Instability Supernova.”
If you don’t know what that is, don’t feel bad, you’re not alone - I’m learning
about this too.
Apparently, according to the theory, what may have happened is that this was the result
of star so massive and hot that it generated antimatter in its core.
That would cause the star to go violently unstable, and undergo repeated bright eruptions
over periods of years.
That process may even repeat over decades before the star’s large final explosion
and collapse to a black hole.
The main problem though is that these Pulsational Pair Instability Supernovae are supposed to
only really occur in the early universe, when the universe was less than about a billion
years old.
This supernova is much closer than that, only about a half billion light years away, so
it’s basically happening today in cosmological timescales.
Another problem is that this supernova was more powerful than most Pulsational Pair Instability
Supernovae are supposed to be so this theory doesn’t fully explain the observations.
So astronomers really don’t know what’s going on here and they’d love to see another
one.
They are going to keep watching this because, well they can.
It stays bright three years after it’s discovered.
So there you go folks, just when you think you understand something, like the deaths
of massive stars, you see something you’ve never seen before that doesn’t fit into
our knowledge of how we think the universe works.
Science is a never-ending journey, it’s always something.
Next, The Giant Magellan Telescope Organization (GMTO) announced that it has started the casting
of the fifth of seven mirrors that will form the heart of the Giant Magellan Telescope
(GMT).
When completed, the GMT will be the largest telescope ever built.
The 25-meter diameter GMT will be built in the Chilean Andes and will be used to study
planets around other stars and to look back to the time when the first galaxies formed.
Sounds a lot like what the JWST will do, only from the ground.
Now listen to this, it’s incredible.
The process of “casting” the giant mirror involves melting nearly 20 tons of glass in
a spinning furnace.
This spinning will give the mirror its initial shape and once cooled, the glass disk will
be polished to its final shape using state-of-the-art technology developed by the University of
Arizona.
The GMT will combine the light from seven of these 8.4 meter mirrors to create a telescope
with an effective aperture 24.5 meters in diameter (80 feet).
With this unique design, the GMT will produce images that are 10 times sharper than those
from the Hubble Space telescope in the infrared region of the spectrum.
This really is a different way to make a mirror, I’ve never heard of anything like this.
The mirrors begin as these pristine blocks of custom manufactured low-expansion E6 glass
from the Ohara Corporation of Japan.
Precisely 17,481 kg of these glass blocks have been placed by hand into a custom-built
furnace pre-loaded with a hexagonal mold.
At the peak of the lengthy casting process, in which the giant furnace spins at up to
five revolutions per minute, the glass is heated to 1165°C (2129°F) for about four
hours until it liquefies and flows into the mold.
The casting process continues as the glass is carefully cooled for three months while
the furnace spins at a slower rate.
The glass then undergoes an extended period of shaping and polishing.
The result of this high-precision process is a mirror that is polished to an accuracy
of one twentieth of a wavelength of light, or less than one thousandth of the width of
a human hair.
Now that’s how you make a mirror.
With this casting, the fifth GMT mirror joins the additional GMT mirrors at various stages
of production in the Mirror Lab.
Polishing of mirror 2’s front surface is well underway; coarse grinding will begin
on the front of the third mirror shortly and mirror number 4, the central mirror, will
soon be ready for coarse grinding following mirror 3.
The first GMT mirror was completed several years ago and was moved to a storage location
in Tucson this September, awaiting the next stage of its journey to Chile.
The glass for mirror 6 has been delivered to Tucson and mirror seven’s glass is on
order from the Ohara factory in Japan.
This telescope, when finished, will be among the largest privately-funded scientific projects
ever and continues a trend that we’re seeing with a lot of these initiatives, like the
Planets Foundation, which hopes to build even larger ground-based scopes to find life in
the universe.
Finally, the Atacama Large Millimetre/Submillimetre Array (ALMA) has made the sharpest observations
yet of a star with the same starting mass as the Sun.
The new images show for the first time details on the surface of the red giant W Hydrae,
320 light years distant in the constellation of Hydra.
What’s important here is that this star is very similar to our own Sun and provides
a glimpse of what will happen to us in about 5 billion years.
Stars like the Sun evolve over timescales of many billion years.
When they reach old age, they puff up and become bigger, cooler and more prone to lose
mass in the form of stellar winds.
As you know, stars manufacture important elements like carbon and nitrogen.
When they reach the red giant stage, these elements are released into space, ready to
be used in subsequent generations of new stars.
ALMA's images provide the clearest view yet of the surface of a red giant with a similar
mass to the Sun.
Earlier sharp images have shown details on much more massive, red supergiant stars like
Betelgeuse and Antares.
These observations have also contained some surprises.
There was the presence of an unexpectedly compact and bright spot astronomers think
provides evidence that the star has surprisingly hot gas in a layer above the star’s surface:
the chromosphere.
The measurements of the bright spot suggest there are powerful shock waves in the star’s
atmosphere that reach higher temperatures than are predicted by current theoretical
models for AGB stars.
Or - and this is interesting as well - this star could have been undergoing a giant flare
when the observations were made.
So while there is much these observations can teach us about what will happen to a star
like our Sun, here’s the part that I found most interesting.
This graphic shows the orbit of the earth (that dotted line) superimposed on the ALMA
image of the star.
Astronomers have never been sure just how large our Sun will get when it expands into
a red giant, some have said it will go out past Jupiter.
But this suggests that our Sun may expand out past Mars and stop before it gets to Jupiter.
Still, no matter what, Earth is in for a really bad day some five billion years from now.
Well, that’s it for this episode Space Fans.
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