Galaxy wars, when is a collection of stars no longer a galaxy?

Friday, 28 January, 2011

Following the recent argument over what constitutes a planet – which famously saw Pluto downgraded in status a few years ago – debate is now raging over whether groups of stars should be considered galaxies when they may in-fact be star clusters instead.

Star clusters and galaxies both contain stars bound together by gravity, but while the members of a star cluster are thought to form simultaneously from a collapsing ball of gas, galaxies have richer histories. In the most popular cosmological model, they form along swathes of dark matter and contain enough gas to form many generations of stars. Yet the distinction is not always clear-cut. Take Omega Centauri, a round swarm of stars that orbits the Milky Way and is visible to the naked eye. It has long been classified as a star cluster, but there is now evidence that it contains multiple generations of stars, suggesting it is actually the remnant of a galaxy.

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Last weekend I classified over three thousand galaxies

Thursday, 1 April, 2010

Having already catalogued some 60 million galaxies across the universe, Galaxy Zoo, a research group founded by US and British astronomers, needs help classifying some 250,000 galaxies that so far remain un-indexed.

Rather than relying on imaging applications though, the astronomers would prefer the assistance of people, as the human “brain is better than even the fastest computer” for such work.

While participants are unable to name any galaxies they classify, I’m sure there is nothing to stop anyone saying they were part of a team that explored the universe.

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Colliding galaxies, an insight into Milkomeda’s formation?

Monday, 13 July, 2009

Eventually our galaxy will collide (or, if you prefer, merge) with the Andromeda galaxy forming a new body some are already calling Milkomeda, but this photo of four galaxies colliding – by the way – at speeds of up to two million miles (or 3.2 million kilometres) an hour, may be indication of what may happen when Milkomeda does form.

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Photos of the night sky, it’s all black and white out there

Friday, 26 June, 2009

Space photographer David Malin has just published a book featuring many of his photos of distant stars, galaxies, and nebulae using only black and white images.

When I started doing photography in the late 1950s, it was essentially all black and white. You could create your own images in the darkroom fairly easily, and that creative process was very rewarding because you could make a picture say exactly what you wanted it to say. I’ve gone back to my roots here to explore again the nice tonal ranges and structures you can fish out in black and white. It’s a kind of journey back. And when I first remember looking at science books as a child, all the galaxies and star forming regions were in black and white. So it’s also nostalgic in a way.

PS: A few of his images can be seen here.

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The chances of colliding with a star are a million to one

Thursday, 19 February, 2009

My recent mentions of the eventual merger/collision of the Milky Way and Andromeda galaxies, giving rise to “Milkomeda”, has prompted some reader questions about the likelihood of a star from Andromeda colliding with the Sun, during the “merger”.

One thing to remember is the collision is billions of years away, should it even happen, but the chances of stars from either galaxy colliding are extremely remote given the astronomical distances between them:

As with all such collisions, it is unlikely that objects such as stars contained within each galaxy will actually collide, as galaxies are in fact very diffuse – the nearest star to the Sun is in fact almost thirty million solar diameters away from the Earth. (If the sun were scaled to the size of an American quarter, 24.26 mm (0.955 in), the next closest quarter/star would be 700 km (475 miles) away.)

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When galaxies collide we’ll be living in Milkomeda

Wednesday, 28 January, 2009

Our galaxy, the Milky Way, is destined to “merge” with our giant neighbour, Andromeda, in about five billion years.

Currently both galaxies are approaching each other at speeds of 120 kilometres (km) per second, and “Milkomeda” is one name that has been dubbed for the combined entity.

Before the collision occurs though both galaxies will fly past each other twice, occurrences that could possibly result in the Sun, and its family of planets, being drawn into the Andromeda system.

There is also a remote 3% chance that the Sun will jump ship and defect to the Andromeda galaxy during the second close passage. “In the night sky, we would then see the Milky Way from a distance,” says Loeb.

Just to put the distances into some perspective, moving at a rate of 120 km per second means covering about 3.8 billion km per year. The planet Neptune is some 4.46 billion km from the Sun, so we are talking about some very, very, vast amounts of space here.

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