aesmael | Entries tagged with stars

Originally published at a denizen's entertainment. You can comment here or there.

Last week seems to have been a good week for news in astronomy. At the least of the sorts that capture my especial interest.

From Universe Today, Spot Discovered On Haumea Rich With Organics And Minerals.

Haumea, one of those planets called dwarfs, is notable for its extremely rapid rotation (a bit less than four hours) distorting its shape well out of spherical and its pair of moons (and the origin of those moons being a probable collision early in Haumea's history which stripped much of its mantle and originated the Haumea collision family). I was thrilled to see such a headline, although on further reading of the article it seems a touch premature:

Possible interpretations of the changes in the light curve are that the spot is richer in minerals and organic compounds, or that it contains a higher fraction of crystalline ice.

So although it appears there is a dark patch on Haumea's surface, we won't know its composition until next year at the earliest. Still, I'm excited to learn just about any new details about these worlds.

Via the Extrasolar Planets Encyclopedia (currently 374 planets and counting), a preprint of a paper submitted to The Astrophysical Journal: The Formation Mechanics of Gas Giants on Wide Orbits.

Presently there are two major theories concerning the formation of giant planets. The core accretion model holds that if a planetesimal can accumulate at least ten Earth masses before the gas of the surrounding protostellar disk dissipates, it will be able to rapidly accumulate a massive envelope of gas. Meanwhile the disk instability model proposes giant planets form when part of the disk becomes unstable and collapses in on itself like a version in miniature of how stars form from giant molecular clouds.

For a while now the core accretion model appears to have prevailed, I think largely because the two models produce different sorts of planets with only a bit of overlap, and most of the planets we have been finding so far suit the core accretion model far better. That is, planets with up to a few times the mass of Jupiter, on orbits less than 10 - 20 AU (Astronomical Units) from their host star.

This paper reminds that there are now planets being found which the disk instability model explains far better than the alternatives - more massive planets approaching the realm of brown dwarves, on orbits too distant for core accretion to have produced them in situ, with orbital dynamics suggesting they were unlikely to have arrived there by scattering from interactions with other planets.

After reading it, I would not be surprised of Fomalhaut b did turn out to originate from core accretion and scattering, but I think they are probably right about the planets of HR 8799 and that there are many more such systems to be found. Would be very interested to learn if there are inner planets to these systems yet undiscovered, and what happens when both planetary formation modes are at work in the same system.

Another quick bit from Universe Today: Smallest Exoplanet Yet Has Rocky Surface. CoRoT-7 b may not turn out to be the smallest planet orbiting an actively fusing star yet discovered, but it is the one with the lowest mass we are currently sure of. The article is definitely worth reading, as some of the details about that planet are amazing.

A picture from Astronomy Picture of the Day, the Andromeda galaxy in UV. Was thrilled to note that in the mouseover comparison, the correlation of UV areas with bright blue starforming areas.

From The Planetary Society, "Richard Kowalski is the first person in history to possess a piece of an object that he discovered in space", an asteroid detected in space and tracked to its impact in Sudan last year. I don't know how I managed not to hear of this at the time it happened, but here is an account from shortly after it happened.

Current Mood: curious

They both photograph stars and analyse the image, attempting to discern such information as life history, companions, or time and manner of demise and contribution to future generations.

Current Mood: amused
Current Music: Pazi

    Planetquest reports on the discovery of the largest known extrasolar planet. TrES-4's mass was found to be only 0.84+/- 0.10 that of Jupiter but its radius is 1.674+/-0.094 Jupiter's. That is, well, large. It works out to ~119,680km (radius, not diameter) if I am lazy and use Wikipedia and Jupiter's equatorial radius.

    Aaaanyway, for a long while Jupiter was thought to be about as large as a non-stellar object could get because as mass is piled onto it (pretend you are an advanced alien civilisation that puts stuff on other stuff for fun), the increase in its gravitational field balances its tendency to expand, so that even brown dwarfs many times Jupiter's mass are nearly the same size. It is only when the object is sufficiently massive for fusion to occur that hydrostatic equilibrium shifts again and the object 9star, now, or young massive brown dwarf) expands to much larger size.

    Well, this is what was thought when the prevailing opinion was that all gas giants exist comfortably far from any stars, much as Jupiter does. Then we discovered the solar system is not as ordinary as we thought and a great many giant planets orbit their stars with suicidal closeness. External heat sources can do the job of internal ones in a pinch, so many of these 'hot jupiters' (yes, that is what they are being called these days, those wacky astronomers - I can imagine people in the distant future talking about jupiter this and jupiter that and not knowing where that particular technical term came from) are larger in size than our Jupiter, even though they tend to be lower in mass.

    Of course in the years since models have been developed to explain the expansion of superheated giant planets, but one of the things that make TrES-4 so interesting is that it is actually larger even than those models predict, so I am very much looking forward to finding out why.

    ...

    People like facts and figures, right? TrES-4 has a density of ~0.2g/cubic cm, roughly the same as balsa wood. It and its host star - which is more massive than Sol and thus entering its giant phase despite being about the same age* - are around 1400 light years distant and its temperature is about 1600 K. Its orbit is only about 4,500,000 km from the surface of its sun and its period is roughly three and a half days.

    Happy now? ^_^

    Love,
          Tricia Fakename

*This world, the same age as our own, is at the end of its natural lifespan. Superheated and boiling away, it will soon be swallowed up and blasted out existence by the death throes of the star which gave birth to it.

Current Mood: excited

    A thought, earlier in the reading than the writing. I have noticed a very strong tendency for readers to only comment on a single aspect of a blog post. Often, indeed, people will remark on the same thing rather than each picking a different topic to follow. I could not say if this is an artefact of following after the first to comment or of a particular part of the post finding better resonance with the readers in general, or to what degree it might be a combination of those (or other?) factors.
    It does tend to make me inclined to separate thoughts into posts rather than paragraphs to better spark discussion (although I also am wary of what I have seen called 'spamming people's friends lists'). Is that bad or good? It is a change in style from my previous unexamined preference. An adaptation to the medium which maybe better accomplishes goals (provoking discussion, sharing ideas, providing learning/enlightenment opportunities for myself), so it may well be good. If I could someday say the state of the world has been improved I might even call it Good but that is rather unrealistic.
    It is a change and on that ground I am inclined to dislike it. Is this because I grew up reading of older modes of discussion and hoped someday to participate in them myself? I think so. I am disappointed but, to refuse to take into account the fact that the world* is changing (I cannot appreciate how much) would be counter-productive. Nor would I know how. Do I write a letter to my friends?
    That blog posts slip away so swiftly is an annoyance. Oh, they are saved and still accessible later but they only hold attention very, very transiently. This might be more a matter of substance than medium. Sometimes when I have written something I am especially pleased with I am tempted to withhold from further posting for a number of days so that it remains more visible, even though anyone who reads what I have to say is using LiveJournal and the flow of their river is little affected by what I do. Should put in a feature request to be able to tag posts into streams of varying priority, then the daily grind can flow on and disappear while topics for discussion remain visible until displaced by more discussion.
    These thoughts are incomplete.

Amusement: Blogging software in a browser with built-in spell-check ability does not recognise 'blog' as a legitimate word.
Further amusement: I suspect I ironically mangled that laughing sentence.

Ami Angelwings Heavenly Comic Rants

Negativity hurts Ami :( [Ami is right. Nominal equality doesn't mean everything is peachy keen now, there is still time needed for (hopefully) social attitudes overall to improve. And spreading negativity, pulling other people down does not seem very helpful to me - I rather thought the idea was to pull people up, so to speak, although if a person is behaving badly/advocating for a harmful position I do thing they should be called on it somehow. Sadly, my opinion is that a large part of this is human nature and not subject to change in the immediate future.]

Ami Angelwings' Heavenly Comic Reviews

Small update :O [*sigh* At least I know where not to spend money]

Astronomy Picture of the Day

Pantheon Earth and Moon [It took me a while to see this as an image of something real.]
3D Face on Mars [I need to make a pair of those red/blue glasses]
Smooth Sections of Asteroid Itokawa [The rubble-pile asteroid collision simulation shown in this link bears passing resemblance to simulations of colliding galaxies. That site looks very interesting. Must revisit. I think this particular APOD is a repeat though, hasn't taken account of the CIA World Factbook move. I am excited to learn what we might discover when Hyabusa returns - we have never brought a sample of an asteroid back to Earth for study before (although there have been some self-deliveries). Note to self: Find out more about these low gravity 'space hopper' probes. Amusement: The Wikipedia article on the 'Brazil Nut Effect' has been edited to mention this picture, since that kind of sorting by size has been proposed as a mechanism to explain the lack of visible craters on the asteroid. I suppose what we need to do now is send another probe to probe its interior with radar.]
A Supply Ship Approaches the Space Station [Just as it says. The blog of one of the astronauts being delivered is here, too bad I did not know about it while it was being written. Photo added to desktop slideshow.]
The Sun in Three Dimensions [Hey! You're missing one!]
Carina Nebula Panorama from Hubble [Eta Carinae is one of my favourite possibly already dead stars. As the article said it did fade dramatically in the 1830s (and if memory serves, had first brightened dramatically). Eta Carinae is one of the most luminous, massive stars we know of. Possibly it is even larger than our theories allow for a star to be - but it is not the most stable of stars, already having blown off an amount of mass equivalent to that of our Sun many times over and producing frequent, enormous eruptions. It is not expected to last long for a star. And it might be a binary! I remember reading a paper in the university library suggesting that a regular variation in X-ray output may be caused by a companion star with a ~5 year orbit, although the amount of dust and gas Eta is giving off, I think, make it impossible for us to observe directly. Eta Carinae's companion might be much smaller than Eta but still be a rare giant among stars - Eta Carinae is in a class of perhaps a dozen out of ~200 million stars in this galaxy. So naturally this is another desktop picture]
Gliese 581 and the Habitable Zone [Yup, they are finally finding these worlds. There will be many, many more to come.]
M81 in Ursa Major [Pretty!]
Young Moon and Sister Stars [I wanted to see this but kept forgetting to look]

Ballastexistenz

And still no blog carnival because... []

But Enough About Me!

Further Ruminations on Girls, Coming of Age, and the Hero's Journey [The often important reminder that, in valuing difference, one must be careful not to devalue the ordinary ('sneering at "the mundanes"'). Read the comments. I want to keep thinking about the topics raised here and they do plenty to keep it going.]
"They didn't want the violence to be real or the truths to be inconvenient." [Refers to this post by Gwyneth Jones|Bold As Love. New word for me: traduce. I am tempted to step away and say I do not have the education or insight to respond to this. Yet, if I do, how will I ever acquire them? I believe I must attempt to engage in order to learn. So I will ponder the first question coming to mind: what else could be considered a success? Is there any other outcome that might be considered a victory for more than immediate visceral gratification? But those questions fail to address the substance of the post. More understanding required. The word grok springs ironically to mind (I get to use that word once more in this post before you are allowed to complain.]

Calvin and Hobbes

2007-04-28 [*smiles* Not that easy]

Devil's Panties

2007-04-28 [:-/ Sure, she's sitting on the mallet, but what is holding the mallet up?]

Dilbert

2007-04-28 [meh]

Order of the Stick

445: A Song for the Departed [I had been trying to wait and see how sad I should be, before Rich Burlew went and had Elan show us.]

Peanuts

2007-04-28 [also meh]

"I hope you see the sun, someday in the darkness"

*The world is humans and their doings, their society? There is more than that, oh yes, but we are all-consuming to ourselves. And this is where we live.

Phil Plait has a post up about NGC 1316, a galaxy careless enough to let four of its stars go supernova in the space of 26 years, two in the past six months. For comparison the average is one per century (Without more information I would assume this is referring to more massive galaxies with active star formation like our own).

I could go on more, I suppose, but pretty much everything is covered at Bad Astronomy. Well, I can add that a galaxy is a very big place and these two supernovae certainly occurred thousands of light years distant from each other. They would have exploded centuries, perhaps millenia apart in time and it is only coincidence we see them at nearly the same time (same for the other two, too).

Current Mood: excited
Current Music: The Steward of Gondor - Howard Shore & Billy Boyd

It is a problem explaining the formation of planets around stars more massive than our Sun. Well, it is a problem not yet solved how they form around any star, but especially the more massive ones. The standard model of planetary formation (Not the Standard Model!*) involves a disk of gas and dust surrounding the star as it forms, and from which the planets form. But during the formation of a massive star it is expected to give off much more, and more energetic radiation than our Sun and less massive stars ever did (the very most massive of stars are not actually the brightest in the visible spectrum - their luminosity peaks in the ultraviolet [!] [I really must write up something about blackbody spectrums, etc.]) and it is thought this might blast away the disk before there is time for planets to form. But now what appears to be such a protoplanetary disk has been found around a massive young star. Alas the main article is also behind a subscription wall (this time at Science) so I cannot get at this one either.

Also, apparently massive stars form in the expected way and not via collisions. Or at least this one appears to be. Well, I was not aware of the alternative idea so, um, good?

*Yes, I think that is funny

Current Mood: complacent
Current Music: nomusic

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