Hello Earthlings.
I’m just going to leave this little string of color photos from Ingenuity (oh you know, the helicopter flying on Mars, duh?) right here for now…
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Too. Cool.
let’s go
volume (4):
15 new (variable) stars discovered in a galaxy just about 11.1 million light-years away (!)
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Let’s talk about “variable stars”. If we had the chance to observe them long enough, probably all the stars in the Milky Way could at some point in their life be considered variable. All that means is that the light from the star varies: sometimes in a rhythmic reliable dance, sometimes erratically, sometimes due to stellar evolution.
There is a multiplicity of variable stars. I really want to call this variable stars (pt 1/tbd) because seriously, truly, really, there are so many different types of variable stars and they’re all f#$%ing cool so we will return here (for sure).
All of these variable stars can be broken into two main types:
Intrinsic variable stars; whose apparent changes in luminosity are due to the inner workings of the star itself
Extrinsic variable stars; whose apparent changes in luminosity are due to some other celestial object passing “in front of” it
Let’s start with extrinsic variable stars. Remember our binary star systems? Some of these two star systems are referred to as eclipsing binaries (simply) due to the fact that one star passes in front of the other from our Earthling point of view. An eclipsing binary is an example of a type of extrinsic variable (scholarly referred to as an eclipsing variable star).
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Another example of an eclipsing variable star could be a stellar system with transiting exoplanets. That is to say that the planet's orbit brings them “in front of” their home star from our Earthling POV. We can measure that dip in brightness from the star and not only is this a method of exoplanet detection, but it is also informative of the home star.
So you can see why I say that any star in the sky could in its lifetime be considered “variable”. To me, what’s really variable is the point from which we can observe all of this data. I find it more interesting that it is only because of where we are looking from, that many of these stars are considered extrinsically variable. The intrinsic variables, however, would be considered variables no matter where you were observing them from.
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The variability of intrinsic variable stars is universal. Observations of an intrinsic variable should, theoretically, measure the same no matter where it is observed from. It is this universality and a distinct relationship between their period and intrinsic luminosity (don’t worry esoteric words we will get to you) that is the reason why intrinsic variables of all sorts are referred to as Standard Candles or Cosmic Yardsticks. Astronomers use these variable stars to calculate distances of galaxies far far far away.
The most well known of the so-called standard candles of the intrinsic group are known as Cepheid(s), after the first of its kind to be discovered. Remember main sequence stars? Cepheids are stars that have evolved off the main sequence, into what is scholarly referred to as the Cepheid instability strip. These variable stars pulsate due to periodic expansion and contraction of the surface layers of the star. They appear to grow bigger (and then smaller) in both diameter and temperature.
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It was Henrietta Swan Leavitt who first noticed the special relationship between period and luminosity for Cepheid variables. In the 1900’s Henrietta was working at the Harvard College Observatory studying photographic plates of the Large (LMC) and Small (SMC) Magellanic Clouds. She compiled a list of 1,777 variable stars from the clouds, 47 of them she would ultimately classify as Cepheids. She noticed that the stars with longer periods appeared brighter than those with shorter periods. Henrietta correctly inferred that since all the stars she had observed were from the same far away cloud they must be relatively the same distance away from Earth. Any difference then, in their brightness, must therefore be related to a difference in absolute magnitude.
The absolute magnitude of a star is the shine that star would have if it were at a distance of 10 parsecs from us. A parsec, contrary to Star Wars belief, is not a measure of time but a measure of great distance. One parsec is approximately equivalent to 3.26 light-years.
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All stars shine, some shine brighter than others, some are far away and some are closer, some stars nearby don’t shine very bright at all while others very far away appear to shine so bright you’d think they were closer to us than a less bright star. With telescope observations, we can detect the apparent magnitude - the rate at which the star appears to shine from our POV. It was quickly realized that to properly compare stars it was prudent to think of them as compared from the same distance.
Think about a really bright star shining from 100 light-years away and think about our sun right here in our sky. If I were to go hijack that really bright star 100 light-years away and paste it into orbit near Pluto, would it outshine the sun? Yes. Yes it would. Even though from our POV the sun appears much brighter than the star living 100 light-years away, the faraway star’s absolute magnitude is probably much greater than that of the sun. Let’s just also call absolute magnitude a stars’ intrinsic luminosity - how bright it actually shines (like, its energy output).
So when Henrietta plotted her results they showed what is known now as the period-luminosity relationship; cepheids with longer periods are intrinsically more luminous than those with shorter periods.
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Very simply put, you can use a star’s apparent luminosity versus its intrinsic luminosity to determine its distance. This is the big hubbub about Cepheids. Because their intrinsic luminosity can be found fairly easily with good observation and can be well compared to others like it, these variables earn their name standard candles and serve as the perfect cosmic yardstick.
I think it’s pretty cool (and kind of funny) that anyone anywhere in the universe who is taking cosmic measurements is probably looking towards all the same Cepheid stars as we are (:P)
Moon Pic of the week (!)
Don’t Miss Out (!)
“With just one polka dot, nothing can be achieved. In the universe, there is the sun, the moon, the earth, and hundreds of millions of stars. All of us live in the unfathomable mystery and infinitude of the universe.” - Yayoi Kusama