Hello,

We noticed you're browsing in private or incognito mode.

To continue reading this article, please exit incognito mode or log in.

Not a subscriber? Subscribe now for unlimited access to online articles.

Emerging Technology from the arXiv

A View from Emerging Technology from the arXiv

Milky Way's Galactic Neighbourhood Puzzles Astronomers

It looks as if the Milky Way and its nearest neighbours make up one of the rarest configurations in the local Universe. Now astronomers are wondering why

  • December 21, 2010

There’s something odd about our galactic neighbourhood, which Sidney van den Bergh at the Herzberg Institute of Astrophysics in Canada highlights today in a short paper.

Astronomers have long known that the Milky Way’s two closest neighbours are the Large and Small Magellanic Clouds, giant clouds of stars, gas and dust called irregular galaxies.

This is strange for two reasons. These galaxies are much younger than ours and may have even formed together. It looks as if they may just be passing by, on their way to somewhere else. Most other galaxies like ours, such as Andromeda, don’t have a single companion like this, so having two seems rather fortunate.

But there’s something else as well. The Large Magellanic cloud is unusually luminous. In fact, there are only two other irregular galaxies in the entire local universe that come close. “In other words the Large Magellanic Cloud seems to be close to the upper luminosity limit for irregular galaxies,” says van den Bergh. That’s unusual too.

In recent years, astronomers have begun to work out just how rare this is. Sky surveys such as the Sloan Digital Sky Survey allow astronomers to work out the distribution of various types of galaxy. They’ve looked at 22581 galaxies like the Milky Way and found that 81% have no satellite galaxies as bright as the Magellanic Clouds, 11% have one such satellite, and only 3.5% host two such satellite galaxies.

That makes the Milky Way very unusual. As van den Bergh puts it: “That the Galaxy should have an irregular companion as luminous as the Large Magellanic Cloud is almost a miracle.”

One of the central tenets of cosmology is the Copernican principle: that we live on an ordinary planet, in an average galaxy, in a mediocre part of the Universe.

But it’s beginning to look as if the Milky Way, or at least its neighbourhood, doesn’t follow that rule at all. So the question for astronomers and cosmologists is why this has come about and what its significance should be. An interesting conundrum.

Ref: arxiv.org/abs/1012.3492: A Strange Mènage Á Trois

Countdown to EmTech Digital 2019. Join us and be the AI leader your company needs.

Register now
Want more award-winning journalism? Subscribe to All Access Digital.
  • All Access Digital {! insider.prices.digital !}*

    {! insider.display.menuOptionsLabel !}

    The digital magazine, plus unlimited site access, our online archive, and The Download delivered to your email in-box each weekday.

    See details+

    12-month subscription

    Unlimited access to all our daily online news and feature stories

    Digital magazine (6 bi-monthly issues)

    Access to entire PDF magazine archive dating back to 1899

    The Download: newsletter delivered daily

/3
You've read of three free articles this month. for unlimited online access. You've read of three free articles this month. for unlimited online access. This is your last free article this month. for unlimited online access. You've read all your free articles this month. for unlimited online access. You've read of three free articles this month. for more, or for unlimited online access. for two more free articles, or for unlimited online access.