T Tauri Stars
Published on Feb 10, 2006 at 2:36 pm.
1 Comment.
Filed under science fiction, stars.
OK. This one is for all you Trekkies out there!
Back a number of years ago, (long enough to be depressing), I was teaching a second semester astronomy class. We were covering star formation, and the lecture was on T Tauri stars. Well, wouldn’t you know it, that week’s episode of Star Trek: Next Generation entitled “Clues†had the Enterprise visiting a T Tauri star! Out of a class of 100 students, several were Trekkies, and saw the episode (I did, too!), and they came to the next class all excited because they caught the reference. It was particularly interesting because that episode got the concept of T Tauri stars right, but never actually said what they were! There is no telling how many people watched that thinking that it was just a Star Trek term that they made up for the show.
Now, for the 95% of you reading this blog who don’t know what a T Tauri star is, I guess that I should explain. First of all, let me explain the name. Some time ago I did a blog entry on how stars got their names. I left a few things out. One was the convention for naming a certain class of stars called variable stars. Despite the impression that the stars are unchanging, they do change over time. Most of the time, these changes are pretty slow, so you never notice them. However, at certain times in a star’s life, it can become unstable (in one fashion or another) and begin to change quickly. The most obvious manifestation of these changes is that the star changes in brightness. Such stars that change in brightness are called variable stars. There are many types of variable stars. Some change due to pulsations in the star, others due to rotational effects, others due to runaway nuclear reactions, and all sorts of other mechanisms. There is even one class of variable stars that change in brightness as carbon crystallizes in their outer layers. They expel these bits of crystalline carbon into space. And yes, by crystalline carbon, I DO mean diamonds.
Once a star is identified as a variable, it can get a variable star designation (actually it is a bit more complicated than that). By convention, the first variable star in a particular constellation is called R. The second is S. The third is T, and so forth. So, T Tauri was the third variable star found in the constellation Taurus. What do you do after you reach Z? Then you go back and double up letters. Not just any two letter combination works — there are rules, but we won’t go into them here. Eventually, you run out of the allowed double letter combinations, and so variables after than get a designation starting with V and a number, as in V395 Tauri. But, I won’t bore you with all that. Suffice it to say that T Tauri is the name for the third variable star in Taurus. It turned out to have a rather characteristic type of variation and color, so any other star that looked and behaved like T Tauri was called a T Tauri star (even though those stars had their own separate variable star designation). I hope that isn’t too confusing for y’all. It’s a pretty awkward system, but I didn’t come up with it!
Many years later, we realized that T Tauri stars were not strictly speaking stars after all. They are what we call protostars. A protostar is a big ball of gas that is in its final stages of collapsing to form a star. When stars form, they form out of a large cloud of interstellar gas called a nebula. Portions of the gas clump up into small dark nodules called Bok globules. The protostar forms inside the globule. The gasses spiral into the protostar through a large disk-like feature surrounding the protostar that we call an accretion disk. Eventually, the protostar gets hot enough to dissipate the remnants of the globule, and we get our first glimpse of the protostar, while it is still settling down to become a star. These protostars vary in brightness, which is why they were initially classified as variable stars. Often the remnants of the accretion disk remain for a while around the protostar, providing a place for planets to form. Such a disk is called a proplyd. The first planets to form would be gas giants, and then smaller rocky planets with rather unpleasant atmospheres. It would take a long time for the atmosphere to evolve into something like our nitrogen-oxygen atmosphere.Â
Anyway, I had just covered all of this in class. Then the episode “Clues†aired. It must have been a repeat, since I looked up the actual date that episode first aired, and that was too early in the semester for me to have gotten to all of this yet. At any rate, for those Trekkies out there, I will give a brief synopsis of the episode. The rest of you can skip past the next paragraph. ;) Â
“Cluesâ€: The Enterprise-D is passing the Ngame Nebula (made up name) and a T-Tauri star is observed. Star formation being of some interest, a probe is dispatched to relay data. Suddenly, the Enterprise is many lightyears away, and time has elapsed for the rest of the galaxy, even though the onboard chronometers show no passage of time and no one remembers any time passing. The probe data shows an icy gas giant planet. Captain Picard and his crew assume that a wormhole had tossed them instantaneously then and there, and so they go about their business. Then, they start finding clues that time had actually passed between when the probe had been sent and when they realized that the ship was somewhere else. The Enterprise returns to investigate the T Tauri star and to see what really happened, only to find that it is not a T Tauri star after all, and the icy giant planet was really an earth-like planet with oxygen-nitrogen atmosphere. The planet is inhabited by advanced aliens who don’t like visitors. So, they had the Enterprise sent far away, and the memories of the event erased from the crew. The onboard instruments are reset, and the data faked to make it look like the ship had instantaneously jumped to the new location and time.Â
OK, now back to astrophysics. The interesting thing is that T Tauri stars, being protostars still forming, would not have earth-like planets. Icy gas giant planets are likely what would be found. The episode, though, did not really explain this, only hinting at the idea that an earth-like planet would be unexpected. T Tauri stars are, in fact, often found near nebulae, as in this episode. Wormholes are a theoretical construct of quantum physics whereby an object could take a shortcut to some other point in spacetime without passing through the spacetime in between. In other words, falling into a wormhole could mean that you reappear somewhere else in the universe at any arbitrary time in the future or past. None of this was really explained. That macroscopic wormholes are improbable, of course, can be ignored in science fiction. So, this was an episode that really appealed to us geeks that knew all the background information behind the story. Hence, my students were all excited to understand what was going on in the story.
-Astroprof
EiRiK on September 20, 2007 at 2:19 am: 1
I finally found the reason of vary brightness for T Tauri Star.
just wanna say thank you