compact object

Stellar Evolution Demystified

/ Emma / 7 Comments

Whaddya know…after what seems like a geological age, we’re finally done with stellar evolution! And we’ve covered a truly ridiculous amount of information.

We’ve covered a star’s relatively gentle, humble beginnings within the collapsing cores of giant molecular clouds (or GMCs). We’ve explored how stars begin fusing hydrogen nuclei for fuel and how their interiors work.

We’ve covered how they evolve across the main sequence, and how they eventually exhaust their fuel, lose stability, and expand into giants.

We’ve delved into the way low- and medium-mass stars quietly expel their atmospheres and shrink into inert balls of carbon called white dwarfs. And we’ve watched as massive stars burst apart in brilliant supernova explosions and then collapse into some of the most extreme objects in the universe, neutron stars and black holes.

Those three end states–white dwarfs, neutron stars, and black holes–are known as compact objects, and we’ve explored them too.

If it all seems super complicated…I understand. But now, just as I did once with types of stars, I’m going to give you an overview to put it all together.

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How to Find a Black Hole

/ Emma / 5 Comments

Okay, good question. How the heck do you find an object that emits no radiation? Astronomers find—and study—just about everything in the universe using the radiation it emits or reflects. So…what happens when the object we’re looking for has such a strong gravitational pull that even light can’t escape?

Well, that’s when we need to turn to the theoretical science behind black holes. What measurable effects do they have on objects in their vicinity? Can we detect them indirectly?

Of course, some of you might be screaming at me that we’ve already photographed a black hole—in visual wavelengths! Yes, astronomers did make that achievement—we now have visual proof that what we’ve been theorizing all along is indeed real.

But that black hole was so faint, it took an interferometer the size of the Earth to image. We had to know exactly where to look in order to get that picture.

So how the heck do we find one in the first place?

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Black Holes: What the Movies Get Wrong

/ Emma / 5 Comments

Any of you recognize this?

To those who don’t, it probably looks like a pretty unimpressive, blurry ring. In fact, this is the first ever image of a black hole, taken with an interferometer the size of the Earth.

If you’re a science geek, you’ve no doubt seen tons of artists’ conceptions of black holes on the internet. Most use a great deal of artistic license. Some of my favorite “images” of black holes used to be the ones that look like ripples in the fabric of space. Imagine my disappointment when I realized that’s not the case at all.

Black holes are singularities—infinitely dense places of zero radius with at least 3 M☉ (solar masses) of star stuff—surrounded by an event horizon, inside of which gravity is so strong that even light cannot escape. That’s why it’s called a black hole.

But they are not “holes” in the usual sense. They are not giant space potholes that you can easily stumble into, and you certainly don’t fall into them the same way you would a pothole.

So…what are black holes really like?

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What is a Black Hole, Really?

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If you’re a sci-fi fan, you’ve probably seen these in movies. And I’m guessing you’ve heard a lot about them in pop culture. The problem is, pop culture and movies don’t do a very good job of describing black holes.

First off, let me clear up a common misconception: Black holes do not act like giant space vacuum cleaners, sucking in everything around them. Describing them as “gobbling up” anything is inaccurate.

The representation in movies that bugs me the most is in J.J. Abrams’ Star Trek reboot, when the bad guy falls into a black hole and the good guys almost get pulled in with him. First of all, please…black holes do not growl. And basically none of what happens in that scene is accurate.

So…what are black holes, really?

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What About Binary Systems?

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In the constellation of Perseus, there is a star named Algol that exists in a binary system. The binary consists of two stars: a massive main-sequence star and a less massive giant.

According to what we’ve explored so far…that doesn’t make any sense.

More massive stars evolve faster than less massive ones. They expand into giants before less massive stars do. In any one binary system out there, we should observe a more massive giant and a less massive main-sequence star, not the other way around.

But the Algol system is not alone in this peculiarity. Over half the stars in the universe are binaries, and in a number of those, the more massive star is still on the main sequence.

Why?

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What are White Dwarfs?

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Now that we’re finally talking about white dwarfs, we’re getting into the really cool stuff.

In my last post, we explored planetary nebulae, and we left off with a question: where does the fast wind that forms planetary nebulae come from? Well, remember that planetary nebulae are formed from the atmospheres of medium-mass stars, but there’s still the stellar interior to worry about.

White dwarfs are objects comparable in size to our own Earth. They are the remains of medium-mass stars like our own sun. Often, you can see a white dwarf at the center of a planetary nebula with a large telescope. Together, they form what’s left of a star after it loses stability completely.

But there’s way more to a white dwarf than that…

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