So of course as soon as I take a trip to LA and am really busy, a whole pile of astronomy news pours out when it had hitherto been a slow week. I suspect a lot of these will have more details at the NAM website, so check there too.
1) 
Omega Centauri may be a galaxy. Omega Cen is a globular cluster, a giant ball of millions of stars. These beehive-looking objects are very pretty and very old; some as old or older than the galaxy itself. The Milky Way has well over 100 of them orbiting it. The thing is, Omega Cen is a lot more massive than any other globular, and astronomers have suspected it’s actually a dwarf galaxy. New studies using Hubble and Gemini South have found an intermediate mass black hole in its core, a black hole bigger than one that forms when a star explodes, but smaller than the ones found in the centers of big galaxies. In this case, it has about 40,000 times the mass of the Sun. These are difficult to form, and harder to find — this one was found using the relative motions of stars near the center of Omega Cen. A black hole of this mass is unexpected in globulars, but is about the right size for a dwarf galaxy. This lends credence to the idea that Omega Cen is misclassified.
2) Astronomers see a nascent world. Astronomers using a radio telescope to observe the nearby low-mass star HL Tau were surprised to see a large clump of material near the star. Turns out it’s a planet forming as we watch! It’s more massive than Jupiter, and twice as far out from HL Tau a Neptune is from the Sun. HL Tau is only 520 light years away, giving us a pretty good view. The disk and star are only 100,000 years old, which is incredibly young to be seeing something like this! For comparison the Earth is 6000 4.6 billion years old.
3) Lightweight black hole. Using a brand new technique, astronomers have identified the lowest mass black hole ever found. Orbiting a star like the Sun, the black hole has an estimated mass of 3.6 times the Sun’s mass, a little more than half the mass of the previously known lightweight hole. The new technique is quite complicated, involving measuring the change in the brightness of X-rays coming from a black hole as it gulps down matter from its companion star. The scientists tested the method using black holes with well-known masses, and their results agreed, so they are confident their new result on this bantam black hole are accurate. This very cool news; the lowest mass a black hole can have is only about 3 times the mass of the Sun (black holes forms when the core of a massive star collapses, and it takes that much mass to make a black hole, otherwise a less-dense neutron star forms), so this one is very near the limit. Studying black holes like this one will tell us a lot about how they form, but we have to find them first! So this method is promising.
OK, that’s it for now. I have to go and do movie-star stuff, and it’s a dead certainty I can’t keep up with the astro-firehose this week will be from the meeting in the UK. Like I said above, go to the NAM site or Universe Today to keep up with the latest.
April 2nd, 2008 at 12:22 pm
This post comes before the woodpecker one in the blog, but doesn’t show up on the feed. It’s almost as if it disappeared into a… black hole? Muhahahahaha!
April 2nd, 2008 at 12:43 pm
Worse than that, this morning the Branding Mars post linked directly to the woodpecker one. Not sure what happened to get this one out of order…
April 2nd, 2008 at 12:47 pm
The observation of a planet in formation around a young star is cool beyond words.
Just think, a little over ten years ago we weren’t sure there were ANY planets outside our solar system. Now we’ve found hundreds and can now watch them as they form.
This is truly a golden age for planet hunting.
April 2nd, 2008 at 1:08 pm
There is some weird timing issue going on, and I’m not sure why. The server appears to be OK, as does my WordPress software. I’m still doing the Skpetology shoot (gloat gloat) so I can’t research this too much right now. hopefully it’ll be easy to fix, because I was kinda hoping to be able to post stuff a few hours in advance and let the software actually publish it at a specific time.
April 2nd, 2008 at 1:15 pm
Just remember, BA, that the passage of time may be relative for servers!
I’m still amazed (and sometimes have trouble believing) what can be observed with a telescope/radio telescope at such distances. Then again, I’m still befuddled by ultrasounds and MRI images…
April 2nd, 2008 at 1:22 pm
What exactly is the objective difference between a “very large globular cluster” and a “very small galaxy”?
April 2nd, 2008 at 1:23 pm
Awesome and awesome!
That’s the extent of my input.
April 2nd, 2008 at 3:40 pm
I got the feeling that this thing is within the Milky Way, although once I re-read the article I couldn’t find it. Maybe because it says that the Milky Way has over 100 of these orbiting it. Anyway, where is this dwarf galaxy located?
April 2nd, 2008 at 4:13 pm
Gotta love a lightweight hole.
April 2nd, 2008 at 4:16 pm
That Omega Cen result is way cool. I spent the past month working on the press release for Gemini (and they were working with ESA/Hubble)… if you go to gemini.edu and look at the bottom, I even get a credit for the finder chart.
Anyway, in going back and forth with Eva Noyola (the PI for the Omega Cen results) to get this press release done and also for an article she’s written on the subject in the next issue of GeminiFocus, it’s pretty clear that she’s on to something and now “all” we need to do is look for more anomalous globulars (more massive than expected, differential star populations) and study their stellar populations, and do some spectroscopy to gather more mass estimates… so, it looks like she’ll be busy for a while!!
You can read more about this at http://www.gemini.edu and I’ve done a little writeup on it at my own blog (see above).
April 2nd, 2008 at 4:30 pm
See! This miniature black hole has been sticking around forever and is now busy gobbling up a whole *star*!
Those wackos kind, altruistic scientists were right to stop ebol Schnitzlerland before they turned on that satanic thigummabob!!!!!eleventyone!!123!
April 2nd, 2008 at 6:29 pm
“…the lowest mass a black hole can have is only about 3 times the mass of the Sun …”
It should be possible to see a smaller black hole due to Hawking Radiation. And secondly, that would be able to tell us a lower limit to the age of the black hole as well.
April 2nd, 2008 at 6:56 pm
What did those NASA press agents do to the science? “With a mass only about 3.8 times greater than our Sun and a diameter of only 15 miles”? Black holes don’t HAVE a diameter!
If we truly have a singularity at the center, then a black hole’s diameter is infinite, but whether that’s true or not is the subject of considerable debate among physicists. In any case, you can’t put a ruler inside the event horizon and see what it measures.
The “obvious” solution of measuring the circumference and dividing by pi only works in Euclidean geometry, and space-time around a black hole’s event horizon is anything but flat!
April 2nd, 2008 at 7:28 pm
Jasso–Hawkings radiation is dim. Really, really dim–it turns out that a 3 solar mass black hole would take about 10^58 times the age of the universe to evaporate, or, in other words, if a 3 sol black hole formed 14 Gy ago, it would have lost something less than 10^-24 grams of mass due to Hawkins radiation.
And this neglects cosmic background radiation–any black hole with mass larger than about the moon is colder than 2.7K, so, as far as I understand it, would gain more mass from absorbing CBR than it looses in Harkings emissions.
On a different topic, is the difference between a galaxy and a globular cluster anything more than nomenclature or an arbitrary qualatitive distinction?
April 2nd, 2008 at 9:19 pm
On the lightweight black hole:
I thought there were possibly smaller black holes created at the beginning of the universe (planet-massed, or mountain-massed, which would have evaporated already). So, three solar masses is just the limit of a black hole created by a collapsing star, but smaller ones might exist from other origins.
Then again, black holes aren’t my thing, so perhaps I’m just confused.
April 2nd, 2008 at 9:31 pm
Anything that isn’t big enough to be called what it could be should be called Plutoid. Global clusters can henceforth be called plutoid galaxies.
Dilettante, I found something that explains the whole black hole diameter thing http://www.astro.uu.nl/~strous/AA/en/antwoorden/zwarte-gaten.html#v379
April 2nd, 2008 at 10:59 pm
Haha, we covered like, 2/3 the same subjects. I just posted a blog (no spam, but it is clickable in my name) that covered the smallest black hole and the IMBH, but I covered a solar tsunami instead of the planet forming. I find weird things interesting, I s’pose =P
April 2nd, 2008 at 11:12 pm
The BA wrote, “Orbiting a star like the Sun, the black hole has an estimated mass of 3.6 times the Sun’s mass, …”. It seems to me that it would be more logical to say that the lower mass object, the star, is orbiting the black hole. The center of mass of the system is certainly much closer to the black hole than to the star. The more massive object is going to have a much smaller orbit which would seem more plausible as the ‘center’ of the star’s orbit.
April 3rd, 2008 at 1:06 am
Omega Centauri…but it looks like a glob! Just a big one….
April 3rd, 2008 at 5:50 am
Jasso said:
““…the lowest mass a black hole can have is only about 3 times the mass of the Sun …”
It should be possible to see a smaller black hole due to Hawking Radiation. And secondly, that would be able to tell us a lower limit to the age of the black hole as well.”
I think, Jasso, that what the BA meant was the smallest black hole that can form when a stellar core collapses will have about 3 solar masses. Any less, and the collapse process cannot form a black hole. This does not mean that small black holes cannot form by other processes, but I have no idea what those processes might be.
April 3rd, 2008 at 8:01 am
According to some (dubious) people in Hawaii, the LHC could be one of the processes to create a black hole. I personally doubt it, but that’s not my field so my opinion is irelevant.
April 3rd, 2008 at 9:12 am
“The scientists tested the method using black holes with well-known masses…”
Wouldn’t “well-theorized masses…” or “well-estimated masses….” be more correct? Can we really “know” the mass of something we’re still not 100% sure even exists or can be identified? I was under the impression that by the purely scientific meaning of the word Black holes (and thus their masses, and measurement thereof) were still Theory.
April 3rd, 2008 at 9:14 am
There are a few scientists who are challenging the black hole concept. They would like to replace it with the concept of a gravastar (GRAvitational VAcuum STAR).
http://en.wikipedia.org/wiki/Gravastar
http://www.space.com/scienceastronomy/astronomy/gravastars_020423.html
Instead of a singularity at the center a gravastar has a spherical shell of exotic matter called Bose-Einstein condensate with nothing inside it. I don’t know if an external observer would be able to tell the difference between a black hole and a gravastar.
April 3rd, 2008 at 6:18 pm
The BA wrote :
“HL Tau is only 520 light years away, giving us a pretty good view. The disk and star are only 100,000 years old, which is incredibly young to be seeing something like this! For comparison the Earth is 6000 (struck through) 4.6 billion years old.”
So … um.. your first answer for Earth’s age is to write 600 years old? Only then do you reconsider it?
Surely not!
I’d reckon that first you think 4.6 billion – the scientifically derived and valid figure then you decide to be “smart” by writing 6000 & striking it through.
To be honest I’m really not sure why ..
Okay, we can poke fun at Kreationists and hammer home again and again that they’re wrong but really I’m not sure that this tactic, esp.applied when the topic has nothing whatsoever to do with the creationists nonsense is really a good idea.
Thanks for the news & blog. Great site!
April 3rd, 2008 at 6:37 pm
# Shifty on 02 Apr 2008 at 3:40 pm said :
“I got the feeling that this thing is within the Milky Way, although once I re-read the article I couldn’t find it. Maybe because it says that the Milky Way has over 100 of these orbiting it. Anyway, where is this dwarf galaxy located?”
Omega Centauri – like other globular clusters – is in the Milky Way’s galactic halo; meaning it orbits in a high, slow orbit travelling a long way above and below the galactic disk in which our Sun orbits. If the Milky Way’s disk was two saucers placed together, theglobulars would be little ballbearings on strings whirling up and downpast the plane of the table!
In the sky, Omega Cen is in the constellation Centaurus which is a southern hemisphere one surrounding the Southern Cross & probably not too visible anywhere much north of Florida. Luckily, I live in Adelaide, South Australia! We get the two best globulars – Omega Centauri &47 Tucanae, the Magellanic Clouds, Canopus and Alpha Centauri (which with Beta Centauri makes thepointers to the Southern Cross), the Coalsack nebula, the Jewel Box cluster, Eta Carinae and more .. Definitely the better of the two hemisphere’s for astronomy!
You may wish to check out James B. Kaler’s website – he has photos of all the various constellations there & heaps of info. on them and especially the various stars. I’m pretty sure he’d have Omega Centauri marked on there – its actually visible to unaided eyesight in any reasonably dark sky. (hence its Bayer or Greek letter designation.)
April 3rd, 2008 at 6:49 pm
Wrote # shane on 02 Apr 2008 at 9:31 pm :
“Anything that isn’t big enough to be called what it could be should be called Plutoid. Global clusters can henceforth be called plutoid galaxies.”
But they’re _already_ called globular clusters & perhaps in some cases dwarf elliptical galaxies! We don’t need to add to the nomenclature confusion!
Pluto’ll always be a planet to me – I think the IAU got that very wrong.
I’d be quite happy to call Pluto, Eris and perhaps even Ceres & Charon planets without the qualifier of “dwarf”. After all a dwarf star is still a star! & the classical planets is an even sillier bit of terminology – seems to me the useful way of applying that is to the 5 original unaided eye “wandering stars” – Jupiter, Venus, Mars, Mercury & Saturn.
If we need to classify planets generally, I’d suggest we use the descriptives :
Terrestrial or rocky eg. Earth, Mercury, Mars,Venus
Gas giant or Jovian eg. Jupiter & Saturn
Ice giant or Neptunean eg. Ouranos & Neptune
Ice dwarf eg. Pluto, Eris, maybe Ceres, Sedna, Varuna etc ..
I really believe the IAU made a serious error inthis definition area at their Prague 2006 (?) meeting & needs to review and correct it with something like the suggested system above.
April 4th, 2008 at 8:55 pm
what’s the latest about the holes on mars?
April 5th, 2008 at 4:15 pm
I read somewhere, probably in science fiction, that there should be teeny-tiny black holes from the Big Bang, maybe all sizes, but the Hawking radiation theory implies there’s no point looking for the little ones now. This might have been in a Larry Niven book; he wrote about attending an address by Stephen Hawking (for real, I believe) who could scare you out of your wits by verbally turning the universe inside out on you – the way Niven told it, anyway. I’m pretty sure -that- was Niven… and he also used to base stories around the latest speculative exotic ideas in cosmology and space science, a hostage to fortune if an innocent researcher quite unmaliciously proved that the thing in question didn’t exist. That would be particularly awkward if it happened before publication.
Medium-size black holes, if I have this straight, may have eaten all the matter nearby them and become invisible. But there would be way more of the very small mass ones. But Professor Hawking says that if so, then they’re gone.
April 5th, 2008 at 10:50 pm
Fascinating news abouit Omega Centauri – some implications and questions I’ve got are :
1) If Omega Centauri is reclassified as a dwarf galaxy does that make it the nearest dwarf elliptical or is the Saggitarius dwarf or another of those captured shredded dwarfs actually closer?
2) If it is a galaxy won’t it join the list of just a handful of galaxies visible to the unaided eye – the two Magellanic Clouds, Andromeda, Triangulum – M33, & now the Omega Centauri dwarf galaxy? Has the Local Group of galaxies gained a new member and, if so, where does Omega Cen sit in the heierachy – would it be the smallest dwarf or is it larger than some of the other very faint dwarfs?
3) Can Omega be considered as being *both* a galaxy and a globular cluster (like eg. Ceres = largest asteroid & dwarf planet) or would we it be better to say instead that it used to be an independent galaxy but has since been transformed via capture (?) into a globular cluster? Can a galaxy be part of another galaxy and how long should it be before a smaller galaxy is considered fusedinto or a component partof a larger galaxy?
4) To be a galaxy does Omega need to boast globular clusters of its own? Does it have – or are there any signs it might have had – its own orbiting globulars or extended stellar halo or even dark matter halo? Which leads on to the question of : Should the IAU be trusted to define what a galaxy is after their botch-up with Pluto!
5) Is it the only object like this or could there be more – both around our galaxy and inside others? What are the implications for other globulars and their evolution? Could there be two separate populations or types of globulars – those that used to be separate galaxies and those that were always part of their primary galaxy?
April 9th, 2008 at 5:51 pm
I don’t think this is the actual definition but they may come to be defined this way: A globular cluster was formed from a single gas cloud and all the stars in it are more or less the same age, but a galaxy comprises multiple gas clouds and multiple generations of stars formed at various times (including, in the case of spiral galaxies, stars still forming even today and in the future.)