[♪ INTRO]
When people talk about space, it’s often
on scales so large they’re almost incomprehensible:
Thousands of light-years. Hundreds of millions of years. Billions of galaxies.
But some of the universe’s most beautiful
sights are much more fleeting,
like planetary nebulas, glowing, colorful
shells
of gas that only last for about 10,000 years
or so.
And this week, a paper published in Nature
Astronomy
reported the first one that appears to be
inside out.
Despite the name, planetary nebulas have nothing
to do with actual planets.
They got their name in the 1700s, when astronomers
saw them
as smears of light in their telescopes, not
single points like stars,
but disk-like objects that looked more like
planets.
We’ve known they’re not planets for a
long time, but the name stuck.
Instead, planetary nebulas are a type of stellar
remnant,
or what’s left over after a star dies.
Stars like our Sun aren’t massive enough
to undergo a
supernova explosion, so their death throes
are far less violent.
The outer layers of the star, or stellar envelope,
are shed into
interstellar space, and the core collapses
into a super dense white dwarf.
The electromagnetic radiation emitted from
that core reacts with
the particles from the envelope and other
matter in the area.
Sometimes those particles absorb the energy
and reemit it
at other wavelengths, producing a rainbow
of colors.
Other times, the photons of light emitted
from the white dwarf are so energetic
they knock electrons off their parent atoms
entirely, creating charged ions.
Normally, the stuff closer to the white dwarf
is more ionized
than the stuff farther away, because it gets
hit with the most radiation.
But this planetary nebula is the first one
we’ve seen
that has it the other way around,
and astronomers think that’s because the
inner shell
is excited by shocks from what’s known as
a “born again” event.
Basically, the stellar remnant at the center,
imaginatively named IRAS 17514-1555,
underwent a sort of thermal pulse and its
nuclear engine fired up again,
expanding the star from a white dwarf back
into a red giant.
Yeah. It’s an undead star.
This isn’t the first “born again” event
we’ve ever seen.
For example, there’s also Sakurai's Object,
which was discovered back in 1996
in the area of the sky near the constellation
Sagittarius.
But this is the first time we’ve seen one
with an inside-out nebula,
and the researchers think it’s happening
as the star
in its center rapidly cools back down from
its second shot at life,
whereas Sakurai’s Object is still heating
up.
In the past 4 decades, IRAS 17514’s brightness
has dropped by a factor of 10,000,
and in the process, it’s been ejecting large
amounts of
carbon-rich material at speeds faster than
the nebula is expanding.
That creates a shockwave in the nebula, which
heats up the material
just in front of it enough to ionize atoms
that usually wouldn’t be.
Meanwhile, less-ionized particles are left
in its wake.
That leads to more highly-ionized material
outside of the less-ionized stuff;
in other words, an inside-out nebula.
But besides being a totally unique object
in the astronomy books,
this planetary nebula can teach us a lot.
For one, it’s a missing piece of the story
of how low-mass stars
turn into metal-rich white dwarfs surrounded
by planetary nebulas.
And according to models, the star that became
IRAS 17514
had a mass only 10% larger than our own Sun.
So we might be looking at what could happen
in our own solar system in billions of years.
We’ll never know for certain, ‘cause we’ll
all be dead by then,
but it’s sometimes good just to know, you
know?
In the meantime, there’s another beautiful
astronomical sight
you can catch this very weekend: The Perseid
meteor shower.
It’s caused by the comet 109P/Swift-Tuttle,
which last passed by Earth in 1992 on its
way around the Sun.
The comet was actually discovered back in 1862,
by Lewis Swift and Horace Tuttle,
but since one orbit takes over
a hundred years to complete,
we didn’t have enough data to predict
when exactly it would come around again.
But each time Swift-Tuttle does, it leaves
a trail of dust in Earth’s orbit.
Every year, our planet crashes into that trail
and some of the tiny pieces
of space debris rain down.
But they do not make it very far.
They strike the Earth’s atmosphere at 59
kilometers per second
and get burned away pretty quickly,
creating a meteor shower.
Meteor showers get their names from where
they appear to come from in the sky.
We see Swift-Tuttle’s remnants
coming from the constellation Perseus,
so it gets the name the “Perseids.”
The Earth has lots of regularly occurring
meteor showers throughout the year.
But since this one happens in August,
when the evening weather is nicer, at least
in the Northern Hemisphere,
the Perseids is one of the more popular.
This year, we entered Swift-Tuttle’s dust
trail back on July 17th,
and won’t leave until August 24th,
but we’ll be entering the densest area on
August 12th.
So this weekend, you can expect to
see about one meteor per minute.
Assuming you don’t have any
clouds raining on your parade,
you’ll be able to see meteors streaking across
all parts of the sky in the Northern Hemisphere.
But they will be more visible in areas with
less light pollution.
And lucky for all of us, one major source
of light pollution, the Moon,
won’t be visible, since it’s a new moon
on Saturday.
So if you can find the time this weekend,
check out what the universe has to offer!
Thanks for watching this episode of
SciShow Space News!
To keep up with the latest discoveries
and learn about
some of the most fascinating
things in the universe,
just go to youtube.com/scishowspace
and subscribe.
Also, if you want to celebrate
your love of space with posters
on your walls or shirts on your torso,
check out DFTBA.com/SciShow
[♪ OUTRO]
