Friday, January 30, 2015

Galactic Herding - How do galaxies join up?

Most galaxies travel through space along with lots of other types, shapes, and sizes. Some group galaxies have mostly ancient stars, while others hang with the new cosmic kids.

So do they all share a common origin? Or just chance alignments? Do galaxy groups pick up “strays” along the way?

A new image from the Gemini Multi-Object Spectrograph (GMOS), at the Gemini North telescope located on Mauna Kea, Hawaii shows different galaxy types at the great distance of 300 million light years away. Of interest is a perfect alignment of three galaxies in a precise equilateral triangle: blue-armed spiral NGC 70 at top, elliptical galaxy NGC 68 to its lower right, and lenticular galaxy NGC 71 to its lower left. 

The massive blue spiral (NGC 70) spans 180,000 light-years or nearly twice the extent of the Milky Way’s reach. Its spiral arms look blue because of active regions of star formation (i.e., young hot stars burn with an intense blue light).

In contrast, NGC 68 (lower right) is a much older system known as an elliptical galaxy. It is about half the size of the blue spiral and hosts little dust and gas, so star formation and spiral are absent; the galaxy’s overall yellowish hue shows most of its stars are old and red. 

Although NGC 71 looks like NGC 68 (smooth glow, below and to the left of NGC 68) it's a lens-shaped galaxy seen face on, so it appears more like a sphere. Lenticular galaxies appear trapped between types: like a spiral galaxy it has a bulge and a disk but no spiral arms; but, like an elliptical galaxy, it is missing dust and gas. Maybe galaxies like NGC 71 were originally spiral systems and somehow lost their interstellar material.

Past the triangle to the lower left is the Group’s fourth brightest member, a barred spiral galaxy known as NGC 72. Its main bar crosses its nucleus with dusty arms that wind from each end of the bar and form a nuclear ring – showing recent star formation. Our Milky Way Galaxy has a similar bar feature nearly 30,000 light-years across, as well as a circumnuclear ring.

This new information gives astronomers and astrophysicists a lot to think about. Apparently in the distant universe all types of galaxies can be friends.
Go science!

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