In the early 1900s there was much debate over how our solar system could have formed. One idea was the nebular hypothesis, made popular by Pierre-Simon Laplace in the late 1700s. In this model stars and planets formed together from a primordial cloud of gas and dust.
Dust to Dust
We are the dust of stars, as Carl Sagan so famously said. The elements in our bodies (with the exception of hydrogen) were formed within stars, and then cast out to the universe when large stars explode as supernovae. Of course simply creating elements by nuclear fusion and sending them flying into the cosmos isn’t quite enough to make stardust. The elements also have to clump into dust particulates. Understanding that process has posed a bit of a challenge, but now a new paper in Nature has observed it happening in real time.
Rainbow Star
When we view stars from the surface of our planet, they appear to twinkle. This is due to turbulence in the air, which creates air fluctuations that cause the starlight to deflect slightly. Since stars appear point-like due to their distance, the small deflections are enough to cause the star to twinkle.
Usually we just notice the variation in brightness, but air also acts like a prism, bending different colors of light by different amounts. So not only do stars appear to vary in brightness, they can also appear to vary in color.
Stars Like Dust
When Carl Sagan said we are all stardust, that knowledge was derived from a long sequence of observations and applied physics. We can see the composition of stars by their starlight. We know that fusion occurs in their cores, and we know that the atoms in our body largely come from stars.
Out of the Blue
The image here is of the very center of the Andromeda galaxy. If you look in the middle of this image, you’ll see a smudge of blue. As first demonstrated in an article in Astrophysical Journal, the central blue region is a collection of about 400 young blue stars. They are concentrated in a region about a light year across, and are moving at about 1,000 km/s.
Chain Reaction
It is often said that we are made of star stuff. Except for hydrogen, the atoms in our bodies were fused in supernovae, and in the cores of stars. What’s not often talked about is just how complex fusion is, and how difficult it is to do, even in the core of a star. Take, for example, the seemingly simple fusion of hydrogen into helium, which is the primary energy source of our Sun.
Disappearing Act
R Coronae Borealis is a dim star in the Northern Crown constellation. It is a yellow supergiant about 6,000 light years away. Normally it is a 6th magnitude star, just on the edge of visibility with the naked eye under a dark, clear sky. But in 2007 the star quickly faded from view, dimming to a magnitude 15 star by 2009. Magnitude is a logarithmic scale, so this is a huge difference in brightness. The star was nearly 4,000 times brighter in 2007 than 2009. Just how a star could fade so drastically in such a short time is a bit of a mystery.
Three is a Magic Number
Yesterday I talked about the star T Tauri, a red star that is transitioning into a main sequence star. The image yesterday was a composite of visible and near infrared images. The image below is a high resolution image at an infrared wavelength known as the K-band. You can see the visible star labeled as T Tau N (T Tauri North). You can also see two smaller stars, labeled Sa and Sb. These two stars don’t emit much light in the visible, so they can only be observed in the infrared. Earlier images didn’t resolve the binary pair, and instead only saw it as a single star (T Tauri South). It has only been in the past few years that we’ve seen them as a binary.
Hybrid
Sometimes in astronomy a weird idea can actually pan out. Suppose you have a neutron star that is absorbed by a red giant. Maybe the two happened to have a chance collision. More likely the neutron star was a close binary with a regular star, and as the star died it swelled to a red giant which engulfed the neutron star. What would happen? Back in the 1970s Kip Thorne and Anna Żytkow studied this hypothetical object, which is why they are now known as Thorne-Żytkow objects, or TZOs.