Hello Space Fans and welcome to the long overdue one hundredth edition of Space Fan News.
This week, astronomers using the Hubble Space Telescope have found compelling evidence of
a planet forming 7.5 billion miles away from its star, a finding that challenges current
theories about planet formation.
Out of the almost 900 confirmed exoplanets found to date, this is the first to be found
so far away from its star.
The suspected planet is orbiting a red dwarf star known as TW Hydrae, located 176 light-years
from Earth in the constellation Hydra the Sea Serpent.
Hubble detected a mysterious gap in a vast protoplanetary disk of gas and dust swirling
around TW Hydrae.
The gap is 1.9 billion miles wide and the disk itself is 41 billion miles wide.
That gap, astronomers believe, was likely caused by a growing, unseen planet that is
sweeping up material and carving out a lane in the disk, kind of like a snow plow.
The planet would be relatively small, at 6 to 28 times more massive than Earth.
Its wide orbit means it is moving slowly around its host star.
If the suspected planet were orbiting in our solar system, it would be roughly twice as
far away as Pluto is from the sun.
Now the interesting thing here is that planets are thought to form over tens of millions
of years.
They buildup slowly, but persistently as they pick up dust, rocks, and gas from the protoplanetary
disk.
And a planet this far away from its star should take more than 200 times longer to form than
say, Jupiter did (which took no more than 10 million years by current estimates) based
on its distance of 500 million miles from the sun.
Jupiter took that long because of its much slower orbital speed and the deficiency of
material in the disk, just like this planet.
So that means it would take a planet this far out from its star 200 million years to
form.
But TW Hydrae is only 8 million years old, making it to young to host a planet like this,
at least according to this theory.
There just hasn't been enough time for a planet to grow through the slow accumulation of smaller
debris.
Complicating things further is that TW Hydrae is only about half as massive as our sun.
According to the astronomers, this is the lowest-mass star for which we've observed
a gap so far out.
An alternative idea suggests that a piece of the disk becomes gravitationally unstable
and collapses on itself.
In this scenario, a planet could form more quickly, in just a few thousand years.
So as you an see, this observation raises a lot of questions but the place to start
is to confirm that there is a planet there at all before they can speculate on how it
formed.
But right now, all they see is a gap.
They aren't sure it's a planet yet.
The team used Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) to
observe the star in near-infrared light.
The researchers then compared the NICMOS images with archival Hubble data and optical and
spectroscopic observations from Hubble's Space Telescope Imaging Spectrograph (STIS).
The team sees the gap at all wavelengths, which indicates it is a structural feature
and not an illusion caused by the instruments or scattered light.
Next, astronomers using the Swiss 1.2-metre Euler telescope at ESO's La Silla Observatory
in Chile have found a new type of variable star.
The discovery was based on the detection of very tiny changes in brightness of stars in
a cluster.
The observations revealed previously unknown properties of these stars that defy current
theories and raise questions about what could be causing those variations.
The new results are based on regular measurements of the brightness of more than three thousand
stars in the open star cluster NGC 3766 over a period of seven years.
The observations found that 36 of the cluster's stars followed an unexpected pattern — they
had tiny regular variations in their brightness at the level of 0.1% of the stars' normal
brightness.
These variations had periods between about two and 20 hours.
The stars are somewhat hotter and brighter than the Sun, but other than that, these stars
are basically unremarkable.
This new class of variable stars is yet to be given a name.
Now there are many stars in the sky that are variable or pulsate; their apparent brightness
changes over time.
How this brightness changes depends on lots of properties of their interiors.
This phenomenon has opened the development of a whole branch of astrophysics called asteroseismology,
where astronomers sort of "listen" to these stellar vibrations, in order to get some idea
of their physical properties and get to know more about their inner workings.
So while the cause of the variability remains unknown, there is one tantalising clue: some
of the stars seem to be rotating very fast.
They spin at speeds that are more than half of their critical velocity, which is the threshold
where stars become unstable and throw off material into space.
Those fast spins will have an effect on their variability, but astronomers have so far been
unable to adequately model how.
I'll keep you posted.
Finally, the least massive galaxy in the known universe has been found.
Known as Segue 2, it contains only about 1,000 stars with a little bit of dark matter surrounding
it, holding it together.
According to James Bullock, a co-author on the paper, finding this galaxy is like 'discovering
an elephant smaller than a mouse'.
Not quite sure what that means.
I'm not sure if he means it's a rare thing or this was like discovering a new kind of
elephant.
Anyway, astronomers have been searching for years for this type of dwarf galaxy, they
have long been predicted to be swarming around the Milky Way.
The fact that we haven't found any has been a major puzzle, and suggested that maybe our
theories about structure formation in the universe was flawed in some big way.
So with only 1,000 stars, why isn't this just a star cluster?
They can contain way more stars than this galaxy has.
The difference is the presence of dark matter.
Galaxies have it, star clusters don't and this tiny galaxy has a halo of the stuff surrounding
it keeping the stars gravitationally bound.
Astronomers promise us that this is a 'tip of the iceberg' observation and we'll likely
find more of these as our telescopes improve.
If you want to learn more about this discovery, Alberto Conti and I will be hosting a Space
Fan Hangout in two weeks on June 25th where we'll have the authors of the paper on hand
to answer any questions you may have so stay tuned.
Follow me on twitter at DeepAstronomy or follow the Space Fan News Google+ page to be notified
of the event.
Well, that's it for this 100th edition, thank you for watching and as always, Keep Looking
Up!