back to article Galaxies to get the Pluto treatment?

Science has no standard definition of a galaxy, and a good one is needed because recent observations have found objects in space that “challenge traditional notions of both galaxies and star clusters.” So say researchers Beth Willman and Jay Strader in a new draft paper, “'Galaxy', Defined” which says that the terms “galaxy” and …

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Does this mean that a large, gravitationally bound, group of stars whose behaviour CAN be explained in terms of baryons and Newton's Laws is NOT a galaxy?

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The situation is a bit different from that of planets, as the notion of dwarf planet was introduced to cover cases like Pluto and the larger Kuiper-belt objects. The notion of a dwarf galaxy has been around much longer. Proper definitions help to avoid confusion.

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But the IAU screwed up big time on the term "dwarf planet." Dr. Alan Stern coined the term in 1991 to refer to a third class of planets in addition to terrestrials and jovians, small planets large enough to be rounded by their own gravity but not large enough to gravitationally dominate their orbits. The IAU misused his term by voting that dwarf planets are not planets at all, a claim that continues to make no sense and be inconsistent with the use of the term "dwarf" in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies.

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Boffin

Re: This is taxonomy - not science

"Everything from 'grain of dust' to quasar follows the same physical laws"

Except they don't, that's the problem. Galaxies (as the proposed definition describes them) only follow Newtonian physics if we assume there is some mass/energy in them that we can't detect - dark matter.

Either dark matter is real and we figure out what it is at some point, or dark matter is the equivalent of Vulcan to our latest theories - something that's covering for our lack of understanding at the moment.

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FAIL

Re: This is taxonomy - not science

@Thing

Horsetwaddle. Science uses precise classification because clarity and organisation is absolutely critical in the sharing of complex knowledge. It doesn't matter a jot whether the classifications are arbitrary or intrinsic. What matters is that scientists understand one another without having to write a paragraph-long explanation each time they employ a poorly-defined term.

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Anonymous Coward

Re: This is taxonomy - not science (Some Beggar)

Come on, own up.

Which muppet downvoted this?

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Happy

Re: This is taxonomy - not science (Some Beggar)

"Which muppet downvoted this?"

I suspect whichever commentard took his comments and went home in a huff...

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Anonymous Coward

Correctness

Shouldn't they be 'dimensionally-challenged galaxies'?

Mmmmm yes, completely full of snark tonight I am.

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Find a galaxy that "sings" and name it Sam... then say

We call thee "SAMSUNG", because Sam sang", which, of course, will lead to the question, "If Sam sung, then what song did Sam sing?"

(For years I've been wanting to post some silliness like this... Thanks for the article, hehehehe!)

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Go

Re: Find a galaxy that "sings" and name it Sam... then say

Then Apple can sue it for having round corners.

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Pluto is a planet

Pluto did NOT lose its planet status. The media is doing a tremendous disservice by continuing to treat the controversial IAU decision of 2006 as fact when it is actually nothing more than one opinion in a very much ongoing debate. Only four percent of the IAU voted on this, and most are not planetary scientists. Their decision was opposed by hundreds of professional astronomers in a formal petition led by New Horizons Principal Investigator Dr. Alan Stern. Stern, the person who first created the term "dwarf planet," intended it to refer to a new class of small planets. He never meant for dwarf planets to not be considered planets at all.

The notion that science happens by decree is ridiculous. The IAU is not the "decider" of what is truth. They messed up big time with Pluto, which is why their definition remains unaccepted by many in the field. The IAU is the last place we should look to for another such decision unless we want a second debacle.

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Boffin

Galaxies have...

Supermassive black holes at their center. That should be the definition, since our models of galaxy formation require this. Then the only problem is defining what "supermassive" means, 100,000 solar masses or 100 million...

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Boffin

Re: Galaxies have...

Not quite - it's accepted that nearly all galaxies have them. Besides, supermassive black holes can exist outside of galactic centres...

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Re: Galaxies have...

No they don't necessarily...

See this article about the work of a friend of mine who has turned his work in the Galaxy Zoo project into a PhD: http://aliceingalaxyland.blogspot.com/2011/01/doctor-proctor-and-irregular-galaxies.html

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