Space Fan News #63: A Solar Twin Located; Star Seen Falling into a Black Hole

Uploaded by tdarnell on 04.05.2012

Hello Space Fans and welcome to another edition of Space Fan News.
We are in the sixties with these bad boys.
It may surprise you to know that of all the solar systems we've found within our galaxy,
there are very few like ours. The vast majority of solar systems we've confirmed have planets
that either orbit very close and very fast around their parent star; or it contains a
bunch of hot Jupiters or it might have some Jupiters followed by some rocky planets, then
more hot Jupiters.
There are 10 billion stars like the Sun in our galaxy, but so far, we haven't found a
single solar system like ours.
But not so fast, we might have our first candidate.
This week Ray Villard wrote a blog piece for Discovery News that caught my attention and
led me to a paper intriguingly entitled, "The remarkable solar twin HIP 56948: a prime target
in the quest for other Earths"
Using observations combined from the ESO's Very Large Array, The Keck telescope and the
Hobby Eberly Telescope, the team used precise radial velocity techniques and lots of detailed
spectra to characterize the star and found that it is very similar to the Sun.
Located only 200 light years away, what's remarkable is that of the 10 billion stars
like our Sun in the galaxy, only about 15% of those are chemically similar to the Sun,
which leads astronomers to think that of all the solar like stars out there, ours isn't
typical - it's in the minority. Our star has chemical anomalies that most other stars like
ours don't have.
Which is weird when you think about it. If our star is strange among other solar type
stars (having chemicals in an abundance others don't seem to have) then maybe it's only from
these 15% of solar like stars that rocky planets can form, I mean, it's possible. But obviously
the Kepler mission will give us better numbers on the frequency of rocky planets around solar-type
stars as more planets are confirmed.
Chemical abundances are important because they determine the raw materials available
to make planets from. For example, HIP 56948 has an unusual abundance of aluminum, calcium,
magnesium and silicon it it - by the same ratio that our Sun has. This is why they're
calling it a twin.
Let's see, 15% of ten billion is one and a half billion stars like our Sun that could
have rocky planets.
Another observation they made is one you've heard me talk about before: radial velocity
measurements of the stars wobble caused by any planets it may have in orbit around it.
Here the news is promising as well, they haven't detected any wobble in the star that could
be caused by a hot Jupiter in orbit, which means the few million miles near the star
is empty of huge gas giants and leaves open the possibility of rocky planets in the habitable
zone and maybe even another Earth.
So obviously, people are going to be watching HIP 56948 pretty carefully in the future.
Who knows, we may find the first solar system like ours in the galaxy.
Next, the supermassive black hole at the center of a galaxy 2.7 billion light years away is
directly observed devouring a star.
OK, so the title to this press release kinda made me cringe: "Black Hole Caught Red-handed
in a Stellar Homicide", but OK, I get it, I guess you gotta try to make headlines catchy.
I wouldn't characterize black holes as murderers though, I don't think a star falling into
a black hole is murder exactly, but what're gonna do?
I have this image of black holes roaming the galaxy now, sneaking around with little hoodies
Anyway, according to the press release, astronomers ave gathered the most direct evidence yet
of a star falling into a supermassive black hole.
You guys already know this, but I'll say it again, supermassive black holes have masses
tens to hundreds of millions of times the Sun and these big suckers are found in the
centers of galaxies causing all kinds of mischief. Including, apparently, stellar homicide.
What they've found is a bright flare in ultraviolet light from the nucleus of a galaxy with a
previously dormant black hole. In June 2010, using NASA's Galex telescope and the PanStaars1
telescope in Haleakala, a bright flare was spotted in a distant galaxy.
Both telescopes continued to monitor the flare as it reached peak brightness a month later
and then slowly began to fade over the next 12 months. The brightening event was similar
to that of a supernova, but the rise to the peak was much slower than that, taking nearly
one and a half months. Supernovae, in contrast, brighten over the course of days.
By measuring the increase in brightness, the astronomers calculated the black hole's mass
to be several million suns, which is comparable to the size of the black hole in our galaxy.
To make sure this flare wasn't due to an active galactic nucleus, they also used Chandra to
look in X rays at the hot gas and they found that the gas did not have the same characteristics
of an AGN burst.
What they think is going on is they have captured observations of a star as it got too close
to the black hole. And, due to the chemical signature of the flare (there was a lot of
helium in it), this may be the second time this star has passed the black hole.
The theory is that this star was very old, nearing the end of its life. As it ran out
of hydrogen, the outer atmosphere expanded into a red giant and that envelope of mostly
hydrogen was sucked into the black hole the first time around.
This simulation shows what they think happened.
As it circled around again in a highly elliptical orbit, all that was left was just a helium
core and as it swung around again it was devoured, with some of the material that didn't get
sucked it being ejected outward at high speed causing the flare.
The observed speed of the gas also linked the material to the black hole's gravitational
pull. Measurements revealed that the gas was moving at more than 20 million miles an hour
(over 32 million kilometers an hour). However, measurements of the speed of gas in the interstellar
medium reveal velocities of only about 224,000 miles an hour (360,000 kilometers an hour).
The place we see these kinds of velocities are in supernova explosions. But the fact
that it is still shining in ultraviolet light is incompatible with any supernova we know.
So there you have it, a black hole in a hoodie murdering a star, seen for the first time.
Well, that's it for this week space fans. Thank you for watching and, as always, Keep
Looking Up!