There’s a lot of gas and dust in the universe. Some of it has coalesced into dark nebulae, such as bok globules that almost look like holes in the starry night. We can observe these by the background light they absorb. Some clouds of dust are close enough to a star that light reflects off them, creating reflection nebulae such as the one near T Tauri. But sometimes a cloud of gas and dust is near a hot star, but too diffuse to scatter light much. In this case it can produce a faint nebula known as an emission nebula.
The Coolest Star
One way that stars are categorized is by temperature. Since the temperature of a star can determine its visual color, this category scheme is known as spectral type. The main categories of spectral type are M, K, G, F, A, B, and O. The coolest stars (red dwarfs) being M, and the hottest stars being O. Our own Sun is a G star.
The Great Eruption
Eta Carinae is a star visible in the southern hemisphere with a rather curious history. It was first cataloged in the 1600s as a 4th magnitude star, but by the time it was given the name Eta Carinae in the 1700s it was a 2nd magnitude star. By the early 1900s it had faded to an 8th magnitude star, but then toward the end of the twentieth century it had brightened to a 5th magnitude star. However its biggest change occurred around 1841, and became known as the great eruption.
Mix It Up
When we look at a cluster of stars, we find that they are chemically similar. That is, the ratio of different elements (or metals in astronomy lingo) in various stars are basically the same. This is pretty much what we expect, since these stars all formed in the same stellar nursery, and haven’t drifted apart from each other. Just as human siblings share similarities due to their common genetic origins, sibling stars share chemical similarities due to their common origin. But what about stars with a common origin that scatter across the galaxy? Do they have a common chemical fingerprint?
Doppelganger
Recently in Astrophysical Journal Letters a paper was published on the oldest “solar twin” yet discovered. The star, HIP 102152, is about 250 light years away from us, and about 4 billion years older than our Sun.
Stellar Noise, Stellar Sounds
NASA’s Kepler space telescope has stopped its initial run of collecting data in its search for new planets, but that doesn’t mean there will be no more new discoveries from that data. A good case in point can be seen from a recent article in Nature that demonstrates a clever way to measure the surface gravity of a star.
Bubble Pop
Between the vast expanse of stars in our galaxy there is diffuse gas, dust and plasma known as the interstellar medium. It has been known for quite some time through its effects on radio waves and other light sources. But making a detailed map of this medium has been difficult.
Not So Super Nova
Last year there was a new nova in the night sky, now officially named Nova Delphini 2013. From Earth, it looked like a fairly dim new star in the constellation Delphinus. Novae such as this one are similar to the more popular supernovae. The popular view of a supernova is that of an exploding star. A large star runs out of hydrogen to fuel, and as a result collapses upon itself. This “core collapse” causes intense nuclear reactions which rip the star apart in a huge explosion, which is why this type of supernova is known as a core-collapse supernova.
Even Odds
In the early moments of the universe, hydrogen and helium were formed through a process known as baryogenesis. Trace amounts of other elements such as lithium were also produced, but none of the heavier elements. This means that the first generation of stars were composed of hydrogen and helium, and it is only through fusion in their cores that the heavier elements we see today were created. The carbon, oxygen and iron in our bodies was produced through that process, which is why it is often said that we are star stuff.