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What Exactly Is a Galaxy?

Posted by Soulskill on from the will-smith-will-figure-it-out dept.

sciencehabit writes "Surprising as it may sound, astronomers don't have an answer to this basic question. There's no agreement on when a collection of stars stops being a cluster and starts being something more. Now, in an echo of the recent wrangling over Pluto's status as a planet, a pair of astrophysicists from Australia and Germany want to start a debate on the issue — and they have even set up a Web site for people to cast their votes." While we're on the subject of galaxies, reader mvar pointed out that astronomers using data from Hubble have spotted what could be a new record holder for the most distant known galaxy, located roughly 13.2 billion light years from Earth.

15 of 225 comments (clear)

  1. Voting? by SilverHatHacker · · Score: 5, Insightful

    It doesn't seem like the definition of a scientific term is something that should be left to a democratic vote. Public opinion with regards to science is never a good thing to rely on (creation vs evolution, naturalistic healing, etc).

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    1. Re:Voting? by pushing-robot · · Score: 4, Funny

      A galaxy is a massive, gravitationally bound system consisting of at least one Stephen Colbert.

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    2. Re:Voting? by Daniel_Staal · · Score: 4, Insightful

      Creation vs evolution is a discussion of theories and facts, and facts aren't really subject to public opinion.

      However, this is just definitions. All we really need is some coherent way to draw the line between the two, and it doesn't really matter what the line is. The comparison to Pluto is apt: it didn't really matter whether Pluto was a planet or not, except that science works best with consistent definitions, and either we could use a definition that included Pluto and a couple dozen (at least) other objects in our solar system, or we could use the definition that excluded all of them, including Pluto. Basically the decision was that there would be less public outcry this way, and it made more 'sense'.

      But it'd have been better to have the discussion earlier, which is what these people are trying to do: Hold the discussion early enough that the results will get used before the public at large get emotionally attached to the one or two border cases.

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    3. Re:Voting? by Fat+Cow · · Score: 4, Insightful

      It doesn't seem like the definition of a scientific term is something that should be left to a democratic vote. Public opinion with regards to science is never a good thing to rely on (creation vs evolution, naturalistic healing, etc).

      It's not really a scientific term. No theories depend on the definition of a galaxy.

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    4. Re:Voting? by icebike · · Score: 4, Interesting

      It doesn't seem like the definition of a scientific term is something that should be left to a democratic vote. Public opinion with regards to science is never a good thing to rely on (creation vs evolution, naturalistic healing, etc).

      But you miss the central point of the story.

      There is no formal definition, scientific or otherwise. Its just a term in common usage with no universally agreed upon definition.

      As such voting is as good a method of arriving at a definition as any other, and certainly a better method than was originally used (namely no method at all).

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    5. Re:Voting? by 56ker · · Score: 3, Funny

      And there was me thinking it was a chocolate bar. :P ;)

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  2. Community standards by paiute · · Score: 3, Funny

    I know a galaxy when I see one.

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  3. Standard for astronomy. by Anonymous+Freak · · Score: 5, Interesting

    Lots of astronomical terms are very vague in their definition. Heck, "planet" was only officially defined a couple years ago.

    There is no "official" difference between "ocean" and "sea", either.

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    1. Re:Standard for astronomy. by bunratty · · Score: 4, Interesting

      It's the same for other subjects. In biology, there's no clear definition of the term species. You can define a species as a group of animals that can reproduce sexually with one another, but as far as I know there's no good definition of species for organisms that reproduce in other ways. Sometimes definitions are completely arbitrary, such as the difference between a tropical storm or a hurricane.

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    2. Re:Standard for astronomy. by Tynin · · Score: 3, Informative

      ...such as the difference between a tropical storm or a hurricane.

      Sorry, but this isn't so.

      Tropical Storm = Distinct rotary circulation, constant wind speed ranges 39-73 miles per hour (34-63 knots).

      Hurricane = Pronounced rotary circulation, constant wind speed of 74 miles per hours (64 knots) or more.

      I'm guessing you don't live in an area that regularly gets hit by these storms, as I really though this was common knowledge. Nothing arbitrary about it, unless we are using different definitions of arbitrary. Source: NOAA.

  4. Generally speaking... by Dan+East · · Score: 3, Funny

    Typically they are something far, far away and a long time ago. At least from our perspective that is.

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  5. Depends on model year by boristdog · · Score: 5, Insightful

    Your older Galaxies had more limited trim packages and slightly smaller engines. After 1969 the engines became larger overall and were available in a wider array of trim.

    The two-door convertible with a 400 cu. inch engine would be my choice.

    Should NOT be confused with an Impala.

    I hope that helps.

  6. Doesn't matter by crow · · Score: 4, Interesting

    How you define "planet" or "galaxy" is very much in the nineteenth century scientific mindset of categorizing everything. Haven't we moved beyond that? Names and categories are useful as a way of generalizing a set of characteristics, but if you don't like a given definition, make up a new term for the set of characteristics that you want to generalize about.

    Language is not scientific, and it never will be. We can have starfish that aren't fish and koala bears that aren't bears, and that's just fine. Scientists need to be concerned about how things work, not what they're called.

  7. Use the Carl Sagan Scale by jameskojiro · · Score: 4, Interesting

    Trillions and Trillions of Stars = Super Galaxy

    Billions and Billions of Stars = Galaxy

    Million and Millions of Stars = Dwarf Galaxy

    Thousands and Thousands of Stars = Stellar Cluster

    Hundreds and Hundreds of Stars = Dwarf Stellar Cluster

    Tens and Tens of Stars = Who gives a shit...

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  8. Re:Supermassive Black Holes? by scharkalvin · · Score: 4, Interesting

    Actually the formation of a black hole in the galaxy center may be the norm for galaxy formation. In fact, it may be a requirement to separate a true galaxy from just a cluster of stars. A true galaxy forms when a huge collection of gas condenses into groups of stars. A young galaxy forms a massive black hole at the center where the collection of gas is the densest. Then the galaxy goes through a Qusar phase where it emits two jets of energy formed by the accretion of matter into the black hole. Once all the nearby matter has been accreted into the black hole the Qusar shuts down.