Tuesday, September 9, 2008

Eyeing up Stellar Oddballs

Welcome back to What's Up?

Finishing up on a quick overview of stars, this month will be all about the stellar oddballs.

You may remember white dwarfs from last month, but let's take a closer look into these weird stars.

A white dwarf is the core of a star left over from when a star like our sun sheds off its outer layers and dies.  A white dwarf that weighs as much as our sun would be the size of the Earth which makes it so dense that if you were to take a sugar cube sized portion it would weigh as much as a hippo!

Stars that are less massive than the sun will leave behind a white dwarf mostly composed of helium, the second lightest element.

Stars that weigh around the same as our sun will leave behind a core made of heavier elements since they have the mass to fuse the lighter elements into somewhat heavier ones.  White dwarfs left over from these sun-like stars will be composed mainly of carbon (sixth lightest element) with some oxygen (eighth lightest) mixed in.  The intense gravity of these little stars causes the atoms to get squished together very closely.  This creates a crystalline structure of carbon.  We call this carbon structure a diamond.

Don't think about putting one of these suckers on a ring quite yet.  They are extremely hot.  They are a little over 100,000 degrees Celsius and take billions upon billions of years to cool down to reasonable temperatures.  

If a white dwarf star gathers up enough material to increase to over 1.4 times the sun's mass it will completely explode, leaving nothing behind.  If the remnant from a star is over that 1.4 solar mass limit at the time of death in a star, it will collapse down even further than a white dwarf.  The little negative electrons will combine with the positive protons creating neutrons.  All of the neutrons in the star will be squished together very tightly so that if you took a teaspoon of this material it would weigh as much as a mountain!

Astronomers, using the creativity they are well known for, gave these stars made of neutrons this name: neutron stars.

Neutron stars are very bizarre stars.  If they spin fast enough they will create immense magnetic fields which get twisted and occasionally release enormous amounts of energy.  These neutron stars are called Magnetars.

Some neutron stars have jets that shoot high energy particles out of their north and south poles and as they spin around the jets point in different directions just like a lighthouse.  When these cosmic lighthouses are pointing their beams in Earth's direction we see them brighten and they appear to pulse as the beam appears and disappears.  These stars are called Pulsars.

When stars get larger than about 3 or 4 solar masses the neutrons stars will collapse down even further.  This is where we get a black hole.

Black holes are truly the weirdest things that exist in our universe.  According to theoretical models (lots of juicy mathematical equations) they are infinitely dense points of mass.  Anything that falls into a black hole can't escape unless it travels faster than the speed of light, which is impossible according to Einstein's Theory of General Relativity.

If someone were to fall into the black hole they would become "spaghettified".  The gravity at their feet would be pulling on them so much more than on their head that they would get stretched out into a long noodle shape and then get torn apart.  If they were somehow able to survive being torn apart they would experience a very interesting effect.

According to Einstein's theory of General Relativity, gravity slows down time.  A clock on Earth actually ticks very slightly slower than it would if it were in space.  This has been tested very accurately with satellites.  If there was someone falling into a black hole and they were sending a signal back to us every second we would see this poor bloke's signal separated by longer and longer time spans.  One second between signals... two seconds between... 3... 4...5... and so on until they were spaced by apart by very large amounts of time and the person just faded away and the signals wouldn't get received anymore.

Before time nearly comes to a stop lets see what's up in this month's sky.

Mercury is at greatest eastern elongation on Sept. 11 which means the best time to observe Mercury would be a few days around that date.

Mars and Venus are also in the western horizon this month.  They will be less than a hand width held at arm's length above Mercury in the sky.

On Sept. 15 will be the full moon and on Sept. 29 will be a new moon.

Finally, on Sept. 22 is the Autumnal Equinox, the first day of fall.

Until next month just look up!

Hey Kids...
Remember about the Phoenix mars lander?  It landed on Mars a little more than three months ago and has been digging around in the dirt to see what's in the soil.  It dug down a few inches and hit ice.  Looking at the ice scientists on Earth found out that the ice used to be liquid.  This means tons of liquid water used to be on Mars!  Sadly, it has gotten so cold that all water has since frozen.  Temperatures on Mars where the Phoenix lander is can dip lower than -80 degrees Celsius!  Hopefully the lander brought a winter coat!

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