Category Archives: astronomy

astronomy, star death

Back in the Saddle

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We just got back from a little time away in Colorado. ‘Twas nice to be there, but is nice to be back home and in the saddle. So, to celebrate, here’s a picture from the Hubble Space Telescope.

The Red Rectangle — a Dying Star Seen By HST
The Red Rectangle — a Dying Star Seen By HST

HST imaged the Red Rectangle some years ago in lower resolution, and returned to it again to capture more details at higher resolution. Now, it’s not really a rectangle, but is shaped more like a fuzzy X. What’s causing the X-star? The star in the center of the Red Rectangle is one that began its life as a star similar to our Sun. It is now nearing the end of its lifetime, and is in the process of ejecting its outer layers to produce the visible nebula. The shedding of the outer layers began about 14,000 years ago.

So, what’s with the ejection of the outer layers? Dying stars like the Sun (and all dying stars, really) go through a process called “mass loss” which involves large amounts of stellar material flowing away from the aging star. In this case the outflows are ejected from the star in two opposing directions. The most amazing thing about this picture are the straight features that appear like rungs on a ladder. These rungs could have formed during successive episodes of mass ejection from the star that have happened like clockwork every few hundred years.

In a few thousand years, the star will have become smaller and hotter, and will begin to release a flood of ultraviolet light into the surrounding nebula; at that time, gas in the nebula will begin to fluoresce, producing what astronomers call a planetary nebula.

astronomy news, galaxies, galaxy interactions

Cosmic Galaxy Ballet

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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!