When a Duck is Not a Duck

Globular  clusters are roughly spherical collections of extremely old stars, and  around 150 of them are scattered around our galaxy. Hubble is one of the  best telescopes for studying these, as its extremely high resolution  lets astronomers see individual stars, even in the crowded core. The  clusters all look very similar, and in Hubble’s images it can be quite  hard to tell them apart – and they all look much like NGC 411, pictured  here. And  yet appearances can be deceptive: NGC 411 is in fact not a globular  cluster, and its stars are not old. It isn’t even in the Milky Way. NGC  411 is classified as an open cluster. Less tightly bound than a  globular cluster, the stars in open clusters tend to drift apart over  time as they age, whereas globulars have survived for well over 10  billion years of galactic history. NGC 411 is a relative youngster — not  much more than a tenth of this age. Far from being a relic of the early  years of the Universe, the stars in NGC 411 are in fact a fraction of  the age of the Sun. The  stars in NGC 411 are all roughly the same age, having formed in one go  from one cloud of gas. But they are not all the same size. Hubble’s  image shows a wide range of colours and brightnesses in the cluster’s  stars. These tell astronomers many facts about the stars, including  their mass, temperature and evolutionary phase. Blue stars, for  instance, have higher surface temperatures than red ones. The  image is a composite produced from ultraviolet, visible and infrared  observations made by Hubble’s Wide Field Camera 3. This filter set lets  the telescope “see” colours slightly further beyond red and the violet  ends of the spectrum.

Image Credit & Copyright: NASA/ESA Hubble Space Telescope.

If it looks like a duck and quacks like a duck…….it may still not be a duck?!! That’s the case here with NGC 411; a globular….well, an open star cluster roughly 200,000 light years distant in the Small Magellanic Cloud (SMC). Ya, that’s fooled quite a few people over the last year or so because this object looks like one of the 150-ish globular star clusters in the Milky Way galaxy. It’s got the shape (roughly), size, ancient star color etc. but not only is this object not in our galaxy; the stars aren’t even old. Most globular clusters contain stars from 10 to 12 billion years old but the stars here are roughly 1.5 billion years old. That means they aren’t even half the age of the Sun, not even close.

There are exceptions to most rules but in the life of globular star clusters there are simply too many young blue stars here to be a globular. Blue stars are much larger thus burn through their fuel and die quickly. If this were a globular there simply wouldn’t be enough fuel left after the billions of years to create the masses of blue stars here. This is also where the age of this cluster comes is determined as well. By studying the bluest stars in the cluster it’s been determined that an age of 1.5 billion years seems genuine. Which, for all intents and purposes is pretty old for an open cluster.

NAME: New General Catalog 411, NGC 411.

WHAT IS IT?: Open star cluster.

HOW FAR AWAY IS IT?: 200,000 light years.

HOW OLD IS IT?: 1.5 billion years old.

APPARENT MAGNITUDE?: A pretty dim 11.

WHERE IS IT? (General): Small Magellanic Cloud (SMC) in the constellation Tucana (The Toucan).

WHERE IS IT? (Exact RA/DEC J2000): RA 01h 07m 55,95s / DEC -71° 46′ 04,5″.

NASA page for this image: http://www.nasa.gov/mission_pages/hubble/science/ngc411.html

ESA Hubble page on this object: http://www.spacetelescope.org/images/potw1303a/

SIMBAD data page on this object: http://simbad.u-strasbg.fr/simbad/sim-id?Ident=NGC+411

Image | This entry was posted in Astronomy (Learning), Astrophotography (DSOs), Images, Star Clusters (Globular-Open) and tagged , , , , , . Bookmark the permalink.

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