Gaia

To get past the blur, you have to leave the atmosphere.

So in 2013, the European Space Agency launched a space observatory called Gaia.

Oh, I've heard of Gaia.

Yeah.

By operating in the vacuum of space, Gaia has been able to precisely map the positions and parallax shifts of well over a billion stars.

It pushed reliable geometric measurements out from a tiny local bubble to distances of many thousands of light years.

A billion stars.

That is just...

The Earth physically shifts by 300 million kilometers over six months.

The Gaia spacecraft is a master of measuring parallax, and it has now done so for millions of stars.

But the further away an object is, the smaller its parallax will be, eventually becoming so small that we can't detect it, even with Gaia.

To get round this, astronomers need a new distance measure, a distance proxy.

And so that's where a special type of star enters the story, one called a Cepheid Variable.

So if then Cepheids came along later, we would likely just dismiss it as a troubled method, especially given the fact that they are usually embedded within bustling galactic disks.

So does this mean that there's no crisis in cosmology then? Well, before we totally give up on that idea, I think we still want to improve our precision just a little bit more.

On the horizon, there are two big data releases from the Gaia spacecraft that promise to improve our parallaxes even further and thus will let us go back and recalibrate that distance ladder just a little bit better.

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This is Gaia BH1, the closest known stellar-mass black hole located in the Milky Way galaxy just over 1,500 light years away.

And this is just one type of black hole.

[laughs] So who wants to see 16 more types of black holes? Yeah, me too.

We're about to get spaghettified by every flavor of black hole, from micro to super-extremal black hole.

Gaia BH1 is a great starting point because we discovered it while completely ignoring it at first.

In 2022, scientists noticed something strange while analyzing the European Space Agency's Gaia mission data.

The star they were studying seemed to be orbiting something invisible.

But scientists have worked hard to solve this embarrassing gap in our knowledge.

So for unpredictable stars, how can you tell how far away they are? The answer is parallax, and that's what our first telescope, Gaia, used as it created a galaxy map over the course of 11 years.

Parallax is the principle that, depending on your point of view, things can appear to be in different places.

You can see an example of this right now by holding up your finger in front of your face.

Things can get a little imprecise.

But how then can we use this method to calculate the distance to a star? The secret is to widen your base viewpoint.

Just as the distance between your eyes can influence the effect of parallax on an object, Gaia viewed stars not just once, but multiple times over the course of a decade.

In that time, the face of our night sky will have changed, as we can see in time lapses like this one, with an exaggeration of 10,000 times.

April 25th of 2018 marks the beginning of just such a leap for much of astronomy.

In the early hours of the morning, the Gaia mission's second data release dropped.

Our understanding of our own galaxy will never be the same again.

[upbeat music] The Gaia satellite was launched in late 2013, entirely built and operated by the European Space Agency.

Its primary goal is to map the stars of the Milky Way with a scale and precision orders of magnitude greater than ever before.

Gaia's predecessor, Hipparcos, cataloged 120,000 stars.

Gaia blows this out of the water with positions, colors, and brightnesses of nearly 1.7 billion stars.

Gaia can see orders of magnitude fainter and further away than previous missions, but its greatest superpower is its precise astrometry.

So thank you.

Last week, we talked about the incredible wealth of data dropped by the Gaia mission.

You guys had a ton to say.

Superuser asks how Gaia compares to the upcoming LSST.

So the Large Synoptic Survey Telescope will indeed be revolutionary.

It does have some overlap with Gaia in that it'll measure light curves, so changes in brightness over time for billions of objects across the entire sky.

But Gaia is really optimized for extreme astrometry, phenomenally accurate position data that actually allows measurements of velocities.

LSST won't do as well in that regard, in part because it's on the ground in the Atacama Andes in Chile, rather than in space.