A Hidden Baby Galaxy in our Cosmic Neighborhood

An international team of astronomers, led by researchers at Japan’s Tohoku University, has just reported finding the faintest satellite galaxy ever seen orbiting our home galaxy, the Milky Way.  All stars are born in great islands or groupings of stars called galaxies.

Big galaxies like the Milky Way are surrounded by smaller “baby galaxies” (or satellite galaxies), some of which collide with it over cosmic times.  About 50 such galaxies are currently known to orbit our Milky Way – with the two “Magellanic Clouds” (discovered by Ferdinand Magellan’s crew) being the most famous of them.

Because many of the smallest galaxies are very faint, they are hard for us to make out.  Remember, we are inside the Milky Way, and so (as we try to look outwards) we always have to observe through the stars and star clusters of our own galaxy.  The faint baby galaxies can be hard to tell apart from clusters or groups of stars in the Milky Way itself. (This is why it’s hard to get a good photo of the Milky Way; we are inside it and so it’s like trying to take a selfie from inside your kidney.  The view is not so clear.)

Still, using the giant Subaru telescope (whose mirror is more than 24 feet wide), the team was able to find the faintest baby galaxy ever found, which is being called Virgo I (since we see it in the constellation of Virgo.)  At an estimated distance of 280,000 lightyears from us, Virgo I was much fainter than earlier surveys for our neighbor galaxies were able to reveal.

The whole Virgo I “dwarf galaxy” is only about 248 lightyears wide.  Compare that to the 100,000 lightyear diameter of the Milky Way! The Magellanic Clouds are estimated to be 7,000 and 14,000 light across.  So you can see that Virgo I really is just a baby. See the tiny smudge it makes on our accompanying image.

But if one such baby galaxy has escaped our notice until now, chances are many others like it may also be out there.  Some of our theories predict that major galaxies like the Milky Way should be surrounded by many more dwarf galaxies that we have seen so far.  Virgo I leads astronomers to think that more may be out there -- just waiting for bigger telescopes and more observations before they are discovered. 

New Hubble Image of Giant Star Nursery

The Hubble Space Telescope folks have just released a beautiful photo of a region where new stars are forming. Called by its catalog number, N11, this region of young stars and reddish glowing gas is in the Large Magellanic Cloud, one of the satellite galaxies that goes around our Milky Way. When you look at the image, bear in mind that the light we are seeing today from this galaxy left it 168,000 years ago. (In other words, the photo shows something 168,000 light years away.)

In the upper left corner, you can see the Rose Nebula, a tight round region in whose hidden center, new stars are being born right now. To give you a sense of scale, that little round gas cloud -- at the very top right -- is about 8 light years across.

In the middle of the image is the more extensive cloud of gas and young stars nicknamed the Bean Nebula (because of its shape.) Several generations of stars have been born in that cloudy region, and their adolescent energy has helped push the gas that gave birth to them into a larger and larger region.

Toward the bottom of the picture, you can see a jewel box of young bluish stars. Many are so hot they actually glow not just with blue and violet light, but with ultraviolet (what tanners call "black light.") Their energy has pushed for a while on any remaining gas from the cloud that gave them birth, so the neighborhood around them shows almost nothing of the reddish glow that signals warmer gas.

N11 is one of the largest nurseries for making stars we have ever observed. It's wonderful to have such a clear colorful image of the whole area, thanks to the remarkable instruments aboard the Hubble.

(And a personal note: the catalog number N11 is from a list of such glowing nebulae first put together in the 1950's by astronomer Karl Henize. Later in life, Henize became a Shuttle astronaut, and when it was his turn to go to space, he was a member of the Board of Directors of the Astronomical Society of the Pacific, where I was the Executive Director. He found that he had enough room in his personal kit to take a banner for the Society into space with him. We didn't have a banner, but when he offered, we of course made one up, real fast. He brought it back from space and presented it to me in a wonderful ceremony at the Society's headquarters (see photo below). It still has a place of pride on the walls of the Society's building in San Francisco.)