Title: We live in a huge bubble! What's Hiding outside The Solar System?
A new study confirmed that Earth is surrounded by a huge bubble. Better said, the whole
solar system is embedded in this vast bubble. And no, it isn't one of those bubbles that we
used to blow when we were kids, it's not a matter of water and soap. In fact, is way bigger. Just to
say, it is so big that, if you had the chance to drive your car to the speed of light and
decided to cross this bubble, it would take to you something like 1000 years. At the speed of light!
Also, this bubble's borders drive the formation of all nearby young
stars. This is exactly what a new study suggests.
But where does this bubble come from? Will it eventually disappear?
And is this a unique feature of the solar system, or do
different star systems own different bubbles? Follow me in this video to get to know the answers
to all of these questions! Let's go.
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Well, let's be clear: the existence of such a bubble was already known for decades.
Astronomers have been referring to it as the “Local Bubble”. It is a giant
void surrounded by thousands of young stars. Some studies were made, but needless to say,
this is a hard topic, and for this reason, much has remained unclear about this bubble.
For example, we don't really know how big it is. Some estimations suggest it should be something
like 1000 light-years in diameter. However, we are not even sure this bubble is a perfect sphere.
In fact, it is likely to have an irregular shape: it seems to be
narrower in the galactic plane, becoming somewhat egg-shaped or elliptical and may
widen above and below the galactic plane, becoming shaped like an hourglass.
What astronomers recently found, however, is that the Local Bubble may support star formation.
What exactly happen is that they saw some star-forming regions lay exactly on the bubble's
surface. As Catherine Zucker, an astronomer at Telescope Science Institute in Baltimore, said:
“We stumbled upon this discovery completely by chance.” Basically, they were very lucky!
But before coming to the study results,
I want to explain how we believe such Bubbles are created in the universe.
Here's the thing: everything starts with a cute star. This star evolves during its life,
and eventually, she's so unlucky to go supernova. For the ones on Earth,
a supernova is a beautiful event to watch, because it can reach high luminosities.
A supernova could be so bright that its light could be compared to the one of a full moon!
So supernovae are stars that suddenly increase drastically in brightness, outshining their own
host galaxies. They reach this brightness in just a few hours and take from weeks to months to fade.
Scientists classify different types of supernovae by their emitted light signatures,
which are called spectra; these show what elements the original
star created and thus released into space after it exploded.
Type Ia supernovae • Their spectra show
very little hydrogen and a lot of carbon. • Astronomers believe this type of supernova
results from a white dwarf that has collected too much material
for its internal pressure to withstand. Type Ib supernovae
• Their spectra contain very little hydrogen; they also show helium.
• Scientists think this type of supernova results from the death of a star
at least 25 times the Sun’s mass.
Type Ic supernovae • Their spectra contain very
little hydrogen or helium.
• They form like a Type Ib supernova. Type II supernovae
• This type of supernova has a lot of hydrogen and helium in its spectrum.
• Astronomers think this type results from the death of a star
larger than eight times our Sun’s mass. Such a star can fuse elements up to iron.
What's left after a supernova is called a supernova remnant.
The supernova remnant is bounded by an expanding shock wave and consists
of ejected material expanding from the explosion,
and the interstellar material it sweeps up and shocks along the way.
There are two common routes to a supernova: either a massive star may run out of fuel,
ceasing to generate fusion energy in its core, and collapse inward under the force of its own
gravity to form a neutron star or a black hole; or a white dwarf star may accrete material from
a companion star until it reaches a critical mass and undergoes a thermonuclear explosion.
In either case, the resulting supernova explosion expels much or all of the stellar material
with velocities as much as 10% the speed of light, which is approximately 30,000 km/s.
These speeds are highly supersonic, so a strong shock wave forms ahead of the ejecta.
That heats the upstream plasma up to temperatures well above millions of K. The shock continuously
slows down over time as it sweeps up the ambient medium, but it can expand over hundreds or
thousands of years and over tens of parsecs before its speed falls below the local sound speed.
One of the best observed young supernova remnants was formed by SN 1987A,
a supernova in the Large Magellanic Cloud that was observed in February 1987.
https://www.grag.org/wp-content/uploads/2018/12/3-1280x640.jpg
Another one is instead the so-called Crab Nebula. Aren't they beautiful?
https://upload.wikimedia.org/wikipedia/commons/thumb/0/00/Crab_Nebula.jpg/280px-Crab_Nebula.jpg
Well, what we think about these bubbles in the universe is that their exceptionally sparse gas,
as we see for example in our Local Bubble,
is indeed the result of supernovae that exploded within the past ten to twenty million years.
The gas remains in an excited state, emitting in the X-ray band. Geminga,
a pulsar in the constellation Gemini, was once thought to be the remnant of a single supernova
that created the Local Bubble, but now multiple supernovae in subgroup B1 of the Pleiades moving
group are thought to have been responsible, becoming what is called a remnant supershell.
So basically the thing is, our solar system is surrounded by
what is thought to be the rest of death stars.
What the study aimed to do was to create a map of the major landmarks in the solar system's galactic
neighbourhood. Scientists analyzed the positions, shapes and motions of dense gases and young stars
within about 650 light-years of the sun. In order to accomplish their goal, Zucker and her team
used data from the most recent Gaia data release. Gaia is an ambitious mission that aims to reveal
the composition, formation and evolution of the Galaxy. It will provide unprecedented
positional and radial velocity measurements with the accuracies needed to produce a stereoscopic
and kinematic census of about one billion stars in our Galaxy and throughout the
Local Group. This amounts to about 1 per cent of the Galactic stellar population.
This huge stellar census will provide the data needed to tackle an enormous range
of important problems related to the origin, structure and evolutionary history of our Galaxy.
For example, Gaia will identify which stars are relics from smaller galaxies long ago ‘swallowed’
by the Milky Way. By watching for the large-scale motion of stars in our Galaxy, it will also probe
the distribution of dark matter, the invisible substance thought to hold our Galaxy together.
The research involved mapping three dimensions of space, three dimensions of motion and a time
dimension. In fact, the universe is tridimensional and stars and gas can move in all directions,
which means they can have velocity components in x,y and z directions.
And we needed time because we wanted to reconstruct the evolution of the bubble and,
more in general, the evolution of the star-forming regions over the past millennia.
This was never done before. Of course,
we had some understanding of it, but most of the studies were just based on
static 2D images of star-forming regions – which means it wasn't so representative of reality.
One thing about the stars in these star-forming regions is that, In a certain sense,
they “remember” where they came from. Do you want to know what it means?
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The great thing about a star is that it “doesn't forget about its origins”, they know exactly
where it came from, and this information is written in physics law and measurements.
Thus, analyzing the motions of these young stars helped the scientists
reconstruct the chain of events behind the creation and growth of the Local Bubble.
They discovered that these stars were travelling mainly straight away from the bubble's surface,
which suggested they were moving because the bubble was expanding over time, just like it
happens to a balloon when you inflate it. From what we know, the Local Bubble is still growing at
a rate of 6.7 kilometres per second. This is quite a slow speed when we consider events in space.
The researchers found that a series of about 15 catastrophic star explosions known as supernovae
likely began taking place near the Local Bubble's centre about 14 million years ago.
"The supernova explosions triggered a shock wave, and this expanding shockwave
subsequently swept up a shell of dense, cool gas — that is, the surface of the
Local Bubble — which has now collapsed to form thousands of new stars," Zucker said.
But why is Solar System right in the middle of the Local Bubble? Well, that's purely due
to chance. When the first supernova took place, Solar System was quite away from it. But Solar
System's travel around the galaxy brought it (by chance) in the middle of the Local Bubble.
The fact that the sun is currently in the middle of the Local Bubble suggests that such
"superbubbles" may be pervasive across the Milky Way. Otherwise, what are the chances
that our sun is right in the middle of one? Basically, a nice comparison could be made
between the Milky Way and Swiss Cheese. Both of them have holes, and the Milky Way
ones were blasted out by supernovae created by poor dying stars.
What scientists are thinking to do now is to map out the locations,
sizes and shapes of a larger number of bubbles in our galaxy. Who knows,
maybe the Local Bubble is currently interacting with other bubbles in our neighbourhood!
However, one difficult challenge could be the age determination of the so-called
“supernova progenitors”.
Supernova progenitors are the “original” stars, which underwent supernova.
The fact is, due to the shock and the conservation of angular momentum,
and depending on the orbital properties of the progenitor, supernova remnants can be
found far away from where the explosion actually happened, and this makes our task more difficult.
New data from the Gaia mission, Gaia Data Release 3, will definitely help, as it will provide 3D
space motions for 30 million stars, a key ingredient in piecing together this puzzle.
"This video ends here! Thanks for watching everyone! What do you think
about the Local Bubble? How would you use them? Let us know in the comments below,
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