Astronomy Three largest stars identified

Discussion in 'Astronomy' started by tablet, Jan 12, 2005.

  1. tablet

    tablet Premium Member

    Astronomers have identified the three biggest stars known to science.

    If they were located in the same place as our own Sun - at the centre of the Solar System - the stars would stretch out further than the orbit of Jupiter. The red "supergiant" stars are more than 1.5 billion km across, pushing the previous record holder, Herschel's "Garnet Star", into fourth place.

    The new research was presented on Monday at the American Astronomical Society meeting in San Diego, US. The three enormous stars from the study are KW Sagitarii (9,800 light-years away), V354 Cephei (9,000 light-years away), and KY Cygni (5,200 light-years away).

    Luminous and cool
    Astronomers compared a sample of 74 red supergiants in the Milky Way. The international team made new observations of the stars from the 2.1m (84 inch) telescope at Kitt Peak National Observatory in Arizona, and the 1.5m (60 inch) telescope at Cerro Tololo Inter-American Observatory, in Chile. With close stars, scientists can calculate stellar sizes from their temperatures and luminosities. Red supergiants are massive stars nearing the ends of their lifetimes. They are comparatively cool, luminous and very large.

    The analysis also yielded the most accurate temperatures yet found for these objects. The temperatures of the coolest red supergiants are about 3,450K (3,177C), or about 10% warmer than previously thought.

    "The significance of this study is that for the first time in many decades there is good agreement between the theory of how large and cool these stars should be, and how large and cool we actually observe them to be," explained Dr Philip Massey, the project's leader.

    "For the past two decades, there has been a significant disagreement." Dr Massey said that there was nothing wrong with the theory. Instead, the observations of the stars themselves had to be improved.

    The study has been submitted for publication in the Astrophysical Journal

    BBC NEWS | Science/Nature | Three largest stars identified (check link for photo)

    hhhhmmmm............ What's your thought on this?
  2. mscbkc070904

    mscbkc070904 Premium Member

    I always wondered why stars are so far away. We see them in the night sky, yet they are so far away. Plus do they actually travel, like move by rotation, orbit one another or what have you.

    As well as, if they can view these stars, can they see if they are any other planetary solar systems near, around those stars.

    [Edited on 1-24-2005 by mscbkc070904]
  3. Mizar

    Mizar Premium Member

    For your first question stars do move... its slow though. Every thing in a galaxy orbits around it. It takes about 100,000,000 years to complete one orbit and thats probaly a low low guess its most likely more like a billion. Stars also move from gravitonal pulls from their planets if they have them or if they are binary (multi star systems llike Mizar;) ) Take a bag and put something in it now hold it and spin in a circle. Even though you more than 100xs its mass the bag still will make you move as it moves around you thats how planets move stars...

    The only way so far to even come close to seeing a planet around a star is through a specail type of immaging. I have been doing a Misson post here about spitzer. Which can find and see planetary disks orbiting stars see this thread....

    Thanks for wondering. Always a joy to do what this site says and
    Deny Ignorance ( Ignorance is just a lack of knowldge and not something bad well ya know....)

    Peace, Hope, and Love--- Mizar
  4. mscbkc070904

    mscbkc070904 Premium Member

    Thanks Mizar, like I have said before, learn something new all the time. Learning is power and knowledge.
  5. JcMinJapan

    JcMinJapan Premium Member

    I will chime in here now, I cannot let Mizar steal all the fun of

    Looking up at the sky and reminding yourself of twinkle twinkle little star is fun and it is actually correct. Stars will twinkle... why? Because they do not give out a constant rate of light. Now, the closest star is 66,000 times farther from us than the Sun. So, the light from that star and it will be 66,000 times fainter. Also take that star that you see in the sky and make it 66,000 times larger. Then you can figure the size and brightness of the star. Just know its distance compared to our sun and multiply it by our sun and you got your answer........ Amazing that the closest star is 66,000 time further than our sun and yet you can still see it!

    Now this leads to a question about the rotation of stars as well. Many people are under the misconception that stars do not rotate. But, this is untrue, our Sun rotates about once every 25 days at the equator and approx. 36 days at the poles. It may seem strange that it is not the same, but you just have to realize that the sun is a fluid and not a solid body, so it can rotate at different speeds in different places.

    Our Sun is considered a G2 star and it rotates at about 2 km/sec. A neutron star is very quick and averages more than 1000 km/sec. But, a Red Giant (100 times larger than our sun) will only rotate at 1 km/sec or slower.

    Mizar is right about the orbit of the Sun in the Galaxy. Our sun is about 24,000 light years from the center of the galaxy and the orbital speed is around 220 km/sec, so it will take about 200,000,000 years for the Sun to orbit the center of the galaxy. You must also realize that the orbit is not exactly circular as well. So, we will travel to different parts of the Galaxy as well. We will pass through the Galactic Plane about once every 35 million years. Wow, this is about the same time as Mass Extinctions happen..... ;) Now, in this glactic plane there is a location called the Orions Arm, we actually only pass through this about every 100 million years. This location has higher chances of supernovas and conditions that can change the Earths atmosphere dramatically. The Sun also completes one revolution of the whole galaxy once every 230 million years or so. You must also realize the the Milky Way is also rotating and we are actually moveing towards the Andromeda galaxy, both of us are moving towards the Virgo Cluster of galaxies.

    Basically, it seems everything is orbiting around something...... Now, that something is the million dollar question... ;)
  6. yourdementia

    yourdementia New Member

    Can someone just clear up for me
    (a) How do we measure space distance (as in the three stars mentioned above.
    (b)How accurate are these diistances that are stated (is there an accepted tolerance )Are they very accurate or are they just a very rough estimation.
  7. JcMinJapan

    JcMinJapan Premium Member

    The distances to stars are more or less educated guesstimates.

    But, that is basically the best we can do with the current technology itself. I would guess that the best way would be for lasers to connect and be able to check the distances, but when a planet is 10,000 light years away, I would say that the time to send a craft there, set it up and then wait 10,000 some odd years for the light to return is not really acceptable. especially when you think that if we sent a probe at only half the speed of light (currently impossible) it would take 20,000 years to just arrive, so in 30,000 years, we may get the correct distance... ;)

    There are numerous ways to check star distances. The two most popular are: "parallax" and "inverse-square law".

    Parallax is a very interesting method as it uses a visual effect. First, let me have you do an experiment. Look at an object about 15 feet away. Now, close one eye. Then change eyes. Do you see the object moving? Ok, now hold your finger about 3 inches from your face. Try the same experiment. You should notice that the finger seems to move a larer distance than the object further away.

    The Earth revolves around the sun and it helps scientists to reproduce this effect. So, by carefully measuring the angle through which the stars appear to move, usually over a 1 year time and calculating the Earths movement as well, they use geometry to estimate the distance.

    The "inverse-square law" -- This is a fairly simple concept that says that if you have two lights and one is further, then the closer one will be brighter than the more distant one. The brightness mathmatically would be the difference in brightness squared. Astronomers use this by finding stars that are very similar in age and composition, then comparing their brightness, they will be able to estimate the distance. So, if a star is 9 time less bright than another star, it must be 3 times farther away.