Hello Space Fans,
This week's news comes to us from another space fan: paleosmoker (where do you guys
come up with these user names, makes mine seem so lame).
Anyway, paleosmoker wanted to know if I knew about a discovery of the coolest brown dwarf
found so far and what I thought about it. He also asked a really good question: what
EXACTLY differentiates a brown dwarf from a large gas giant?
So, I went to the link he provided which took me here. This is from gizmodo and it outlines
the discovery of a brown dwarf star with a surface temperature of only 97 degrees Celsius.
Then, doing what bloggers do, they compared it to a piping hot cup of coffee.
But, look what they had originally called this post: "a star so cold you can actually
lick it"
But they must have later changed it to read "so cold you could drink it"
Good thing, because I don't know about you, but unless you're licking a chocolate ice
cream cone, there's not a lot of "brown" things that would make for good licking.
Anyway that post led me to this National Geographic page where they discuss this discovery in
a little more detail.
Brown dwarfs (dwarves?) are strange things. They aren't really stars because they don't
'shine', its more of a 'glow' or a 'warming'. There isn't any fusion going on because they
aren't massive enough.
Remember, stars of all kinds along with gas giants and planets, form from coalescing gasses,
mostly hydrogen. What you end up with depends on how much gas coalesced. If enough gas collects
to form an object heavy enough to squeeze the atoms together and ignite hydrogen, then
we have a star. The kind of star you get, again, depends on the amount of stuff that
collected.
There are pretty well defined numbers for the amount of gas that needs to collect to
form a star, and it turns out to be an amount equal to around 75% that of the Sun. This
much gas would create something called a red dwarf, the coolest star that can be created
and it has a surface temperature of about 4,000 degrees.
BTW, All temps I talk about from here on will be in Kelvin, the standard unit for temperature
in astronomy. Google can do the conversions into Celsius or Fahrenheit for you if you're
interested.
Red dwarf stars are extremely interesting because they shine for trillions of years,
they will be the last stars left in the universe. I find these so interesting, I'm creating
a video about them called "The Embers of Creation", so be on the lookout for that.
Back to brown dwarfs. Whenever there isn't enough gas accretion to start fusion in a
star, we get something else, something that doesn't shine through fusion but the friction
of compressing gas still creates heat.
The objects that get created from this process are more ambiguous because they could be either
brown dwarfs or red giant.
They are hard to see through a telescope and classifying them is tricky. Basically, brown
dwarfs have temperatures that are essentially anything less than that of a red dwarf: 3000,
2000 down to just a few hundred degrees Kelvin. which is where this discovery comes in.
As I mentioned briefly, using the Keck telescope, astronomers found a brown dwarf with a surface
temperature of only 370 degrees, so this isn't a star, and it's currently the record holder
for the coolest brown dwarf to date.
What makes it interesting is that the body they found is so cool, it blurs the line between
a gas giant planet and a brown dwarf.
It's hard to really know what to call a brown dwarf: they aren't stars, but the MIGHT be
gas giants.
After all, there have been Jupiter-like planets found that are so hot they approach 500 degrees.
Why aren't they considered brown dwarfs? So this discovery muddies the waters a bit.
For reference, our Jupiter is only about 150 degrees, which is pretty cold, but that's
still more energy than it gets from the sun.
Which brings up another thing, even though these gas giants and brown dwarves aren't
stars, they do still shine, or rather, glow. They are bright in the infrared, so telescopes
like Spitzer are great for locating them. In fact, the Nat geo post mentioned something
about an even cooler brown dwarf than this one, at about 350 degrees that was seen by
Spitzer.
If confirmed, then THAT discovery will hold the record.
So you see, astronomers are still trying to sort all this out. About all that IS clear
is the distinction between what makes a star and what doesn't - stars radiate energy from
atomic fusion. There's a lot more work to be done with those objects that didn't quite
have enough mass to make it that far.
This research will apparently be coming out in a future Astrophysical Journal paper (astronomers
call it ApJ), I couldn't find out which one.
That's it for now Space Fans, thanks for watching and
Keep Looking Up!