Orion Proplyds

The Orion Proplyds were first discovered by the Hubble Space Telescope. Astronomers expected the Orion nebula to be a host for lots of star formation, and were amazed to see that Hubble could resolve individual young stars. The Proplyds are young stars surrounded by a gaseous circumstellar disk . In the image of the Orion Nebula above, the proplyds are enlarged so you can see the bright central star surrounded by a dark oval shaped ring. The disks appear dark because they are absorbing the light emitted by the nebula, and re-emitting it in the infrared, a wavelength of light that does not appear bright in these images. Portions of these disks will eventually fall onto the star, and the rest will either form planets, or be dispersed back into the nebula. Astronomers are using these, and other images of young stars, to learn about how stars form and how planetary systems evolve.

Image Credit:

NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA), the Hubble Space Telescope Orion Treasury Project Team and L. Ricci (ESO)

Hertzsprung-Russell diagram

 

The Hertzsprung-Russell, or HR, diagram is the number one tool of astronomers. Basically, the HR diagram is graph that relates observable quantities of a star such as temperature, brightness and amount of light emitted . We can use this information to group stars into different categories, called spectral types, which we label by the letters OBAFGKM (As random as it seems, there is some logic behind the lettering. I'll explain in a later post). After years of observations, astronomers have discovered an age sequence that is often drawn over the HR diagram (the line in the graph above). After a star is born, it begins on the main sequence at a moderate brightness and temperature. Over time, the star evolves into a giant or supergiant star and changes its position on the HR diagram, heading towards the upper right hand corner where temperature and brightness are high. When the star dies, it plummets leftward and down on the HR diagram, getting colder and dimmer.

The beauty of the HR diagram is this: Astronomers can use telescopes to measure the brightness, amount of light emitted, and temperature of a star. They then place it on the HR diagram and viola we now know its rough age and spectral type! We can then compare it to stars of the same type and age and learn so much more about the star, just by looking at one graph. Such a wonderful tool!

Star Formation

 

 

Ever wonder how stars form? Astronomers have been thinking about that for quite a while, and are pretty sure they have a good idea about how it works. Stars form out of giants clouds of gas and dust in space. The tiny particles bump into each other until they stick and form a large ball of gas. This protostar, as astronomers call it, gravitationally attracts the cloud of gas surrounding it and increases in size until most of the gas has fallen onto the star. What's left is a big ball of gas surrounded by a disk of dust particles which accretes (falls onto) the star. Some of the dust in this circumstellar disk will stick together to form rocks, and a few may even grow big enough to be planets! After about 10 Million years (yes million!) the star will accrete most of the dust and become a "young adult" star, or Zero Age Main Sequence star. The star is now big enough and hot enough to burn Hydrogen in its core (left side of diagram). If the star doesn't accrete enough gas and dust to become large enough to burn hydrogen, it becomes a brown dwarf (right side of diagram). Most of the stars that you see in the night sky are average main sequence  stars of various sizes and ages.