Posted on 04/03/2019 2:52:41 PM PDT by LibWhacker
UNSW astronomers have shown that binary stars – two stars locked in orbit around each other – reflect light as well as radiating it, revealing new ways for their detection.
One of the first things we learn in astronomy is that some of the objects in the sky (the Sun and the stars) produce their own light, whereas others (the Moon and the planets) are only visible because they reflect light from the Sun.
But do the Sun and the stars also reflect some of the light that falls on them?
This is a question that scientists from UNSW Sydney and Western Sydney University wanted to find out, which quite surprisingly, has been little studied by astronomers.
In their paper published in Nature Astronomy, the researchers showed that stars do indeed reflect light, and that this reflected light could be a useful tool for astronomers.
Stellar reflection is most significant in a close binary system, where two stars are in orbit about each other. Such binary systems are believed common, with most of the stars in the universe thought to have binary companions.
The scientists studied the bright star Spica (Alpha Virginis), which is actually two hot stars orbiting each other with a period of only four days. They found that the light of the star is polarised in a way that varies as the stars move around in their orbits.
Professor Jeremy Bailey, from UNSW's School of Physics, said that normally, light from a star is unpolarised, meaning it vibrates in more than one plane. But when light from one star reflects that of another, it will become polarised, with the vibrations of light waves now traveling in a single plain.
He said it is a similar process to the way light is polarised when it reflects off a water or glass surface, allowing us to reduce the glare using polarised sunglasses.
"We were able to determine that the amount of polarisation we observed was exactly that predicted for a reflected light model," Professor Bailey said.
"Our modelling showed that stars are actually quite poor reflectors of light. The Sun, for example, reflects less that 0.1 percent of the light falling on it.
"However, for hotter stars, such as the components of Spica, with temperatures of 20,000 to 25,000 degrees Kelvin, the amount of reflection increases to a few per cent. The total amount of reflected light coming from the Spica system is, however, still very small."
Professor Bailey said the reason why this discovery was important was because it will now allow astronomers to measure properties of stars that they can't easily measure for single stars.
"It provides a way of detecting binary systems that could not be detected by other methods – particularly binaries with face-on orbits – and a way of measuring masses for a wider range of binaries than is currently possible," he said.
"Single stars don't have a light source nearby (such as the binary companion) and so there is no way we could measure the small amount of reflected light."
According to Professor Bailey, what makes the observation of stellar reflected light possible is the fact that the light is highly polarised and measurable with the very sensitive astronomical polarimeters that he and his UNSW colleagues have developed.
"For this work we used three different telescopes including UNSW's own observatory, which is located on campus. The small 35cm telescope here was used to make the majority of observations included in this study," he said.
Professor Bailey said he and his fellow researchers are now testing their techniques on other binary systems and believes the polarisation technique could open up new opportunities for the study of binary stars.
"We expect it to work even better for hotter stars, and it could be used to find binary systems that are not detectable by other methods, and to study binary star orbits and properties," he said.
By the way, I just remembered this, a million or so years from now the Orion Nebula will be a bright star cluster, much brighter than the Pleiades. Collectively, the brightest thing in the sky besides the sun and moon. But I don’t know if this matters, not being a million years in the future.
I’m going to take on your question, though I definitely do not claim to be smarter than you. So you might want to stop reading right here, lol!
All stars are “like” our sun in that they put out their own light because of nuclear fusion taking place in their cores. But the similarity ends there. There is a huge variance, or variability, in the population of stars out there, in their mass, temperature, size, age, etc. There are short YouTube videos that show the variance in the size of stars.
I think most if not all stars are believed to have planets. But of course, some stars might not have planets because none ever formed (hard to believe), or were swept out of existence by nearby orbiting binary companions.
I’m no astronomer but I once stayed in a Holiday Inn Express next to a bowling alley.
I figure thusly. Our sun contains, as I understand, around 99.8% of the solar system’s mass. Jupiter contains most of the rest. The remainder was still enough to spawn Saturn and the other planets and asteroids and moons.
So, unless there are really, really greedy and efficient stars out there, I’m going to say that virtually every star has at least one rocky planet-sized thing revolving around it, either from leftover atoms or wandering planets that happened by and got captured during the several-billion years the star may have been around.
Earl Anthony (RIP) would have concurred, I’m sure.
Anyone disagree?
There is that, too.
The Nebular theory says that spin is a factor. If a star forms with almost no spin at all, very little leftover debris should be present. What qualifies as a ‘planet’? Pluto doesn’t pass only because it hasn’t cleared its orbit. A system with very little leftover debris won’t contain any planets according to our definition.
More like 90%. 3/4 of all stars are red dwarfs, not even visible from earth. Another 12% are K class. The sun is a brightish G class.
This is old news. If you study Algol (THE eclipsing binary) with detailed photometey, you can see the effects of the bright star being eclipsed by the dimmer, then they get brighter as the light from the brighter star reflects off the dimmer, then there is a dimming as the dimmer star goes into eclipse, cutting off the reflected light from the dimmer star.
Not all stars will have planets, but, a star is a star.
The variations from one star to another comes from age, volume and location.
Really old stars tend to be red stars, big stars tend to age rapidly, and, stars in orbit around each other tend to have weird things happen due to gravity (small, dense stars drawing matter off the bigger, less dense stars).
Right you are, thanks! For some reason, 75% was stuck in my brain. That’ll teach me to always double check my facts before putting them down on paper! Getting old is a b***h!
Can’t afford to stay at a Holiday Inn Express, so I had to look up Nebular Theory. Quite interesting. Thanks.
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I'm going to SPARE you a rebuttal Larry and just say that your comment was a STRIKE out......
Don’t double check your facts. 75% was close enough for most. I’m just a nit picker today it seems.
You’re not going to pin that on me!
Yeah, in a nutshell, whatever debris doesn’t share a ‘common’ angular momentum will collide, cancel out, and fall to the center. Our own sun must have formed from a nebula that had some spin applied to it, from a passing star or whatever. As the nebula collapsed under gravity, it spun faster like a ballerina, and anything not sharing the ‘preferred’ spin didn’t survive long. But that’s only a tiny percentage of the total mass.
You're lucky you're my friend so I'll spare you any further strikes against your comment.
This isn’t new at all. I’ve been teaching this in my astronomy class for years. It is a standard part of binary star light curve analysis. Has been for many years.
“...the Orion Nebula, which is a star factory.”
That’s the one. :)
“But I don’t know if this matters, not being a million years in the future.”
I’m marking my Calendar! We’ll have a beautiful view of it, ‘from above.’ :)
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