Most stars in the Universe are small and insignificant
and they will eventually fizzle out without much drama
But a few light up the sky when they die,
and in the process, they don't just tell us about the lives of stars:
they create the building blocks of life
and help us to unravel the whole history of the Universe.
Episode 64: It all ends with a bang!
...The incineration of Dr. J
Presented by Dr J, aka Dr Joe Liske
There are something like 200 billion stars in our galaxy, the Milky Way
Although nobody really knows exactly how many
One thing that is known though, is that a tiny fraction of these stars
has a disproportionate effect on the rest of the galaxy
Similar stars in other galaxies have taught us much of what we know about
the evolution of the Universe
They are the stars that end their lives as supernovae,
a topic in astronomy to which Hubble has made great contributions
since it was launched in 1990.
Now supernovae come in two broad categories
To understand what's going on in the first category,
you have to realise that a star is actually a very finely balanced thing
The pressure from the nuclear reactions at the centre of the star
is balanced by the star's gravity
Now when a really massive star runs out of nuclear fuel,
the pressure at its centre drops dramatically,
and the star collapses in on itself
and then explodes!
The other type of supernova involves white dwarf stars
which are the remnants of stars like our own Sun.
Now normally, a white dwarf is a pretty stable thing
but, if one lies close to another star,
it can actually pull matter off its neighbour
thereby gradually increasing its mass
...until finally...
...it reaches the critical mass for a thermonuclear...
explosion!
Supernovae are rare
A galaxy like ours can only expect a few every century
The last one to be seen in the Milky Way was in 1604
observed by the great astronomer Johannes Kepler, a few years before the invention of the telescope
Now we know that since then, a number of supernova events
have taken place in the Milky Way
because we can see the debris left behind by the explosions
But we never got to see the explosions themselves
because they were shrouded by dust at the time
and so the fact remains that no supernova inside the Milky Way
has been directly observed since the invention of the telescope.
Instead of just sitting around and waiting for one,
astronomers have decided to increase their odds
by widening the search far beyond our own galaxy
And since we're talking about a very small and distant phenomenon,
we need a telescope that can deliver extremely precise images:
a telescope like Hubble.
The most famous supernova that Hubble has directly observed
came with the death of a giant star in the Large Magellanic Cloud
The light from the initial blast first reached Earth in 1987,
a few years before Hubble's launch.
But Hubble's images of the evolving supernova over the quarter of a century since then
have become the gold standard for understanding this event
Astronomers have been able to study the complex explosion in great detail
showing how the shock from the exploding star is interacting with the gas that surrounds the star,
making it light up
More distant supernovae can't be observed in the same kind of detail as 1987A,
but Hubble is still a great help
For example, because Hubble has been in orbit for more than 20 years now,
astronomers have been able to make before and after images of galaxies,
which allows them to search for the progenitors of supernovae
Now these types of observations potentially tell us
a lot about the conditions of the progenitors just prior to the explosion
As well as telling us about the star that has just died,
supernovae are powerful tools for probing the cosmos
The supernovae that come from exploding white dwarfs
have a peculiar property: they all have the same intrinsic brightness
This means that how bright they appear to a telescope is a measure of how distant they are,
much like a street light looks bright when you're near it, and dim when you're far away
Supernovae are extremely bright
in fact, they are so bright that they usually outshine their entire host galaxies
and that is why it's relatively easy to detect them, even out to large cosmological distances.
In 2011, the Nobel Prize in Physics was awarded to two teams
that measured the brightness of many supernovae to map out their distances
and what they found was that the faraway supernovae were surprisingly faint
which could only mean that they were even more distant than expected
Now, we already knew that the Universe was expanding
but what this research proved was that the expansion is in fact accelerating
and that came as a complete surprise.
Now this is really cutting-edge science
and astronomers continue to study distant supernovae
to better understand the expansion of the cosmos
and Hubble plays a big part in this game;
It just recently hit another milestone when it spotted the most distant supernova yet discovered of this type
it is so far away that its light has taken more than 9 billion years to reach us —
that's about two thirds the age of the Universe.
Closer to home, Hubble has played a big role in imaging the wreckage left behind by supernovae
even though a supernova is only bright for a short period of time,
and its shock waves only propagate visibly for a few years,
the dusty clouds left over can last for millennia.
Their effect on the surrounding interstellar gas lasts even longer
and that means that although no supernovae in our galaxy have ever been observed with any telescope,
plenty of supernova remnants have been.
Hubble's sharp images of their complex structures
help to chart the processes involved in their violent formation
What's more, the clouds of debris are an important reminder of the huge role that supernova play in shaping everything around us
Nuclear reactions inside stars, and in these explosions, are the source of most of the elements found in nature,
including the carbon in our bodies, the oxygen we breathe,
and the iron and silicon on the planet we live on.
And so, although they tell us a lot about the past and future expansion of the Universe,
supernovae also teach us something even more profound.
They literally tell us where we came from.
This is Dr. J, signing off for the Hubblecast.
Once again, nature has surprised us beyond our wildest imagination.
Hubblecast is produced by ESA/Hubble at the the European Southern Observatory in Germany.
The Hubble mission is a project of international cooperation between NASA and the European Space Agency.
www.spacetelescope.org
Transcribed by ESA/Hubble. Translation: --