Category Archives: astronomy

astronomy, astronomy research, Helix Nebula, Infrared astronomy, planetary nebulae, star death, stars, stellar evolution

Staring into the Eye of Star Death

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Visiting the Helix

One of the often-asked questions astronomers get is “What will happen when the Sun dies?”  It’s an obvious concern, since whatever happens to the Sun will affect Earth, but it’s not an immediate concern.  The death of the Sun isn’t going to happen for another few billion years yet, so we don’t have to worry about facing it grow larger during its red giant stage and then shrink down to become a tiny ghost of its former brilliance.  Many, many generations of humans will live and die on our planet before future astronomers will start to detect the first instabilities that indicate the Sun’s upcoming demise.

There are stars like the Sun out there in space that have already gone through the death process, and so astronomers study them to understand what our star will look like when it finally gets down to the serious business of stardeath. One of the objects they have studied quite a bit is called the Helix Nebula.

ESO’s VISTA telescope, at the Paranal Observatory in Chile, has captured a striking new image of the Helix Nebula. This picture, taken in infrared light, reveals strands of cold nebular gas that are invisible in images taken in visible light, as well as bringing to light a rich background of stars and galaxies.

The Helix was created as a Sun-like star reached the final stages of its life.  It began to lose its outer layers of gas, which you can see in the image above as they expand into space.  What’s left of the star appears as a tiny blue dot at the center of shell of material surrounding it. That ring spreads out over an area about four light-years across (almost the distance between the Sun and the nearest star in the Alpha Centauri system.  This infrared view shows the extent of the gas cloud.

The nebula is made up of of dust, ionized material and molecular gas. it’s all being heated up by ultraviolet light streaming out from the central star (which is very hot).  Notice the details in the cloud—there are clumpy, comet-shaped objects called cometary knots.  They aren’t really comets, but they look similar to comets with their tails blowing out in the solar wind. In this case, the knots are  strands of molecular hydrogen being shaped by the flow of high-energy radiation streaming out from the dying star. Even though they look small, each is about the size of our solar system.

This, in a nutshell (or a gas shell) is about how our Sun will look billions of years from now. Perhaps our descendants will watch it all unfold from a planet around neighboring star, and take similar pictures with their orbiting space telescopes.

Want to know more about this image. Check out the European Southern Observatory site for more details and an array of downloadable images.

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The Flickering Universe

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The Ever-changing Lights in the Sky

When you go out and look up at the night sky, you see stars. If it’s out, you can see the Moon, and if you know where to look you can also spot planets.  Sometimes asteroids flare across the field of view, and occasionally there’s a comet out there.  If you’re a frequent skygazer, you already know that the view changes over time.  Really avid stargazers also know that stars can vary in their brightness–and those that do are called variable stars.  Other stars explode.  They flare up into brilliance very quickly, and then fade away. Some time later, if you look at the area of space where the star was, using a good-sized telescope and special instruments, you can spot the remains of the star blasting out into space. Those are called supernovae.

The brightening and dimming of stars actually holds clues to activities and processes in the cosmos that help us understand such things as star birth, star death, the distances to galaxies, and even the expansion rate of the universe. So, it’s no surprise that astronomers want to pay attention to the flickering universe of stars.  In particular, astronomers at the California Institute of Technology have been paying attention to the varying levels of light from stars and other celestial objects; in fact, they’ve released data on 200 million of them!   One of the scientists is S. George Djorgovski, a professor of astronomy at Caltech and principal investigator on  survey of variable objects called the Catalina Real-time Transient Survey. He’s a fellow whose work I’ve admired since I worked on the Griffith Observatory exhibits and his “Big Picture” was a focus of my writing for several weeks. He explained why astronomers survey objects that flicker in the dark. “Exploring variable objects and transient phenomena like stellar explosions is one of the most vibrant and growing research areas in astrophysics,” he said.  “In many cases, this yields unique information needed to understand these objects.”

A map of CRTS discoveries. Courtesy Caltech.

The data set includes more than a thousand supernovae, as well as hundreds of so-called cataclysmic variables. These are stars that periodically brighten up in what looks like a catastrophic outburst, only to quiet down after a period of time. The survey also shows pairs of stars in which one spills matter onto another. Such a star is called a white dwarf. There are also tens of thousands of other variable stars; and dwarf novae, which are binary stars that dramatically change in brightness.

The survey takes repeated images of large areas of the sky. By comparing them to previous images, the survey can monitor the brightness of about half-billion objects. This process helps astronomers search out objects that dramatically brighten. Our galaxy–and others–are filled with the flickerings of star life, star death, and everything in between, giving astronomers a treasure trove of data that will help them understand what’s out there.

The CRTS is part of a larger umbrella project called the Catalina Sky Survey, which also searches out near-Earth objects (asteroids that could pose a threat to our planet).  They, too, have changing brightnesses, which are clues to their surface features and makeup.

If you want to know more about how astronomers are chasing down the dimmings and brightenings of the sky, check out the Catalina Sky Survey and the news released today about the Transient survey. There are discoveries in those distant flickerings!