Category Archives: galaxies

astronomy news, galaxies, galaxy interactions

Cosmic Galaxy Ballet

Leave a comment
Courtesy the Very Large Telescope
Courtesy the Very Large Telescope

As astronomers gaze across the deeps of space and time, they run across scenes like this one — where two (or more) galaxies just get too close to each other for comfort. When this happens, sometimes galaxies end up colliding.

The European Southern Observatory’s Very Large Telescope caught a glimpse of a cosmic tango taking place 190 million light-years away in the direction of the southern hemisphere constellation Pavo, the Peacock. And, like Hubble’s spectacular image of a ring galaxy (created by yet another collision), this VLT image was taken to celebrate another telescopic anniversary — the VLT’s fifth birthday.

So what’s happening in this scene?

NGC 6769 (the one on the upper right) is a spiral galaxy with very tightly wound spiral arms. Its neighbor (NGC 6770) has two major spiral arms. One looks rather straight and points towards the outer disc of NGC 6769. NGC 6770 is also peculiar because it shows two comparatively straight dark lanes and a fainter arc that curves towards the third galaxy toward the bottom of the image, called NGC 6771 (below). Stars and gas have been stripped off of both NGC 6769 and NGC 6770, and they’re starting to form a common envelope around them. Some folks have suggested it looks like the shape of a Devil’s Mask. There might also be a tenuous bridge between NGC 6769 and NGC 6771. All of these features are there because there’s strong gravitational interaction between the three galaxies.

Well, you might think that such a collision would destroy the galaxies and any chances for the normal things that galaxies do (like host star-forming regions).

Not… quite…

There is a true baby-star boom going on in this scene. A cosmic catastrophe like this one normally results in the formation of many new stars, which you can see in the blueish clouds that highlight the spiral arms in NGC 6769 and NGC 6770. There are many sites of star-forming regions.

VLT, and other telescopes (including HST) are studying a great many cosmic collisions like this one to help scientists figure out how and why galaxies form, evolve, and change over time. There’ll no doubt be more cool pix like this one in the years to come!

astronomy news, galaxies, subaru observatory

The Unblinking Eye

Leave a comment
Our eye on the universe, courtesy NASA and the Apollo 17 astronaut crew.
Our eye on the universe, courtesy NASA and the Apollo 17 astronaut crew.

As you sit in front of the computer reading this, you’re riding along on the largest telescope in the universe (that we know of). Oh, we’re not all sitting on a huge reflecting dish or anything like that. But, we do share surface of the planet with hundreds of observatories. The result is that there isn’t a moment of the day when all parts of the sky in every direction aren’t being studied by a telescope somewhere, somehow. That’s pretty amazing until you stop to think about how many telescopes there are in the world — including all the amateur gear! And, if you rise up a few hundred km into space, we have another whole collection of space-based “eyes on the sky.”

The Big Island of Hawai’i is home to a great collection of observatories, among them the Gemini installation, the Keck Observatory, the James Clerk Maxwell Telescope, the University of Hawaii 2.3-meter telescope, and many others. The National Observatory of Japan has an installation up there with the others on Mauna Kea: the Subaru telescope. I used a couple of their lovely images in my book. Here’s their latest.

Sextans A
Sextans A

It’s the Sextans A galaxy, a dwarf Irregular galaxy — a close neighbor to the Milky Way at only 5 million light years away. Here’s what the Subaru folks have to say about their image:

“Young blue stars and older yellow and red stars shine against a dark sky like jewels in a treasure chest in this image of Sextans A from Subaru Telescope?s prime focus camera Suprime-Cam. Sextans A is a dwarf irregular galaxy belonging to a group of galaxies called the Antlia-Sextans group 5 million light years from Earth. Even though five million light years is quite distant (50 billion billion kilometers or 30 billion billion miles), only about 40 galaxies are closer to our own Milky Way galaxy than Sextans A. The Antlia-Sextans group is the closest neighbor of the Local Group, which includes both our own Milky Way the Andromeda Galaxy.

Irregular galaxies do not have a regular symmetric shape like spiral or elliptical galaxies. Dwarf irregular galaxies containing only 100 million to a billion stars are the most common type of irregular galaxy. One main characteristic of dwarf irregular galaxies, other than their shape, is vigorous ongoing star formation. Sextans A has a mass comparable to only 100 million stars, one thousandth of the Milky Way, but contains a comparatively large amount of gas and dust, the raw ingredients for stars and planets. In the center of Sextans A is a high concentration of neutral hydrogen gas that serves as a reservoir for the formation of new stars. The Suprime-Cam image shows both young stars (blue) old stars (red) near the center of Sextans A where there is a large reservoir of neutral hydrogen gas and star formation is most vigorous. The green color highlights hydrogen gas ionized by radiation (HII regions) from the blue-hot young stars.

Many dwarf irregular galaxies are surrounded by neutral hydrogen gas that extends far beyond where the galaxy?s starlight fades away. Observations with radio telescopes have confirmed that Sextans A is no exception. The origin of this hydrogen gas and its effect on star formation are still unsolved puzzles. Yutaka Komiyama from Subaru Telescope, the observer of Sextans A, is now working on a solution using the Suprime-Cam data.”