This illustrates the orbits of more than 150,000 asteroids seen by Gaia as part of its data release 3. The orbits shown here extend from the inner solar system to the orbit of Jupiter. Courtesy ESA/Gaia/DPAC; CC BY-SA 3.0 IGO
The amazing Gaia mission to chart stars in the Milky Way Galaxy is also an expert asteroid hunter. Now, astronomers are reporting its success at spotting more moons of asteroids in our solar system. Once the Gaia data from its release 3 are confirmed, those observations will add 352 more binary asteroids to the known count. That nearly doubles the known number of asteroids with moons and previous Gaia data releases also revealed asteroids in its survey.
Artist impression of ESA's Gaia satellite observing the Milky Way (Credit : ESA/ATG medialab; Milky Way: ESA/Gaia/DPAC)
For over ten years, the ESA’s Gaia Observatoryhas monitored the proper motion, luminosity, temperature, and composition of over a billion stars throughout our Milky Way galaxy and beyond. This data will be used to construct the largest and most precise 3D map of the cosmos ever made and provide insight into the origins, structure, and evolutionary history of our galaxy. Unfortunately, this sophisticated astrometry telescope is positioned at the Sun-Earth L2 Lagrange Point, far beyond the protection of Earth’s atmosphere and magnetosphere.
As a result, Gaia has experienced two major hazards in recent months that could endanger the mission. These included a micrometeoroid impact in April that disrupted some of Gaia‘s very sensitive sensors. This was followed by a solar storm in May—the strongest in 20 years—that caused electrical problems for the mission. These two incidents could threaten Gaia‘s ability to continue mapping stars, planets, comets, asteroids, quasars, and other objects in the Universe until its planned completion date of 2025.
Artist's impression of the ESA's Gaia Observatory. Credit: ESA
The ESA launched Gaia in 2013 with one overarching goal: to map more than one billion stars in the Milky Way. Its vast collection of data is frequently used in published research. Gaia is an ambitious mission, though it seldom makes headlines on its own.
Artist’s impression of the Gaia spacecraft detecting artificial signals from a distant star system. In this synchronization scheme, the star system's inhabitants send the signal shortly after witnessing a supernova, which is also seen by telescopes on Earth. (Credit: Danielle Futselaar / Breakthrough Listen)
The European Space Agency’s Gaia Observatoryhas been operating steadily at the Earth-Sun L2 Lagrange Point for almost a decade. As an astrometry mission, Gaia aims to gather data on the positions, proper motion, and velocity of stars, exoplanets, and objects in the Milky Way and tens of thousands of neighboring galaxies. By the end of its primary mission (scheduled to end in 2025), Gaia will have observed an estimated 1 billion astronomical objects, leading to the creation of the most precise 3D space catalog ever made.
To date, the ESA has conducted three data releases from the Gaia mission, the latest (DR3) released in June 2022. In addition to the breakthroughs these releases have allowed, scientists are finding additional applications for this astrometric data. In a recent study, a team of astronomers suggested that the variable star catalog from the Gaia Data Release 3 could be used to assist in the Search for Extraterrestrial Intelligence (SETI). By synchronizing the search for transmissions with conspicuous events (like a supernova!), scientists could narrow the search for extraterrestrial transmissions.
Direct images of the extrasolar planet, AF Lep b (white spot around 10 o’clock), orbiting its host star (center) taken in Dec. 2021 and Feb. 2023 using the W. M. Keck Observatory’s 10-meter telescope in Hawai?i. (Credit: Kyle Franson, University of Texas at Austin/W. M. Keck Observatory)
In a recent study published in The Astrophysical Journal Letters, a team of astronomers used the W. M. Keck Observatory on Maunakea, Hawai?i Island to identify exoplanet, AF Lep b, which is three times the mass of Jupiter orbiting a Sun-sized star located approximately 87.5 light-years from Earth. What makes this discovery unique is AF Lep b is the first exoplanet discovered using a method called astrometry, which involves measuring unexpected, miniscule changes in the position of a star relative to nearby stars, which could indicate another object, an exoplanet, is causing gravitational tugs on its parent star.
Gaia BH1 is a Sun-like star co-orbiting with a black hole estimated at 10 times the Sun's mass. Credit: ESO/L. Calcada
In 1916, Karl Schwarzchild theorized the existence of black holes as a resolution to Einstein’s field equations for his Theory of General Relativity. By the mid-20th century, astronomers began detecting black holes for the first time using indirect methods, which consisted of observing their effects on surrounding objects and space. Since the 1980s, scientists have studied supermassive black holes (SMBHs), which reside at the center of most massive galaxies in the Universe. And by April 2019, the Event Horizon Telescope (EHT) collaboration released the first image ever taken of an SMBH.
These observations are an opportunity to test the laws of physics under the most extreme conditions and offer insights into the forces that shaped the Universe. According to a recent study, an international research team relied on data from the ESA’s Gaia Observatoryto observe a Sun-like star with strange orbital characteristics. Due to the nature of its orbit, the team concluded that it must be part of a black hole binary system. This makes it the nearest black hole to our Solar System and implies the existence of a sizable population of dormant black holes in our galaxy.
The thing with black holes is they’re hard to see. Typically we can only detect their presence when we can detect their gravitational pull. And if there are rogue black holes simply traveling throughout the galaxy and not tied to another luminous astronomical, it would be fiendishly hard to detect them. But now we have a new potential data set to do so.
Gaia just released its massive 3rd data set that contains astrometry data for over 1.5 billion stars, about 1% of the total number of stars in the galaxy. According to a new paper by Jeff Andrews of the University of Florida and Northwestern University, it might be possible for Gaia to detect perturbances caused by a rogue black hole briefly interacting with one of the 1.5 billion stars in the catalog. Unfortunately, it’s just not very likely that any such interaction actually took place during Gaia’s observing time.
Artist's concept of Earth-like exoplanets, which (according to new research) need to strike the careful balance between water and landmass. Credit: NASA
As of this article’s writing, NASA has indicated that 5,030 extrasolar planets have been confirmed in 3,772 systems, with another 8,974 candidates awaiting confirmation. With next-generation instruments like the James Webb Space Telescope (JWST) coming online, the number and diversity of confirmed exoplanets are expected to grow exponentially. In particular, astronomers anticipate that the number of known terrestrial planets and Super-Earths will drastically increase.
In the coming years, the opportunities for exoplanet studies will increase considerably as thousands more are discovered using various methods. In a recent study, a team led by the Chinese Academy of Sciences (CAS) described a new space-telescope concept known as the Closeby Habitable Exoplanet Survey (CHES). This proposed observatory will search for Earth-like planets in the habitable zones (HZs) of Sun-like stars within approximately 33 light-years (10 parsecs) using a method known as micro-arcsecond relative astrometry.
The night sky, is the night sky, is the night sky. The constellations you learned as a child are the same constellations that you see today. Ancient people recognized these same constellations. Oh sure, they might not have had the same name for it, but essentially, we see what they saw.
But when you see animations of galaxies, especially as they come together and collide, you see the stars buzzing around like angry bees. We know that the stars can have motions, and yet, we don’t see them moving?
How fast are they moving, and will we ever be able to tell?
Stars, of course, do move. It’s just that the distances are so great that it’s very difficult to tell. But astronomers have been studying their position for thousands of years. Tracking the position and movements of the stars is known as astrometry.
We trace the history of astrometry back to 190 BC, when the ancient Greek astronomer Hipparchus first created a catalog of the 850 brightest stars in the sky and their position. His student Ptolemy followed up with his own observations of the night sky, creating his important document: the Almagest.
Printed rendition of a geocentric cosmological model from Cosmographia, Antwerp, 1539. Credit: Wikipedia Commons/Fastfission
In the Almagest, Ptolemy laid out his theory for an Earth-centric Universe, with the Moon, Sun, planets and stars in concentric crystal spheres that rotated around the planet. He was wrong about the Universe, of course, but his charts and tables were incredibly accurate, measuring the brightness and location of more than 1,000 stars.
A thousand years later, the Arabic astronomer Abd al-Rahman al-Sufi completed an even more detailed measurement of the sky using an astrolabe.
One of the most famous astronomers in history was the Danish Tycho Brahe. He was renowned for his ability to measure the position of stars, and built incredibly precise instruments for the time to do the job. He measured the positions of stars to within 15 to 35 arcseconds of accuracy. Just for comparison, a human hair, held 10 meters away is an arcsecond wide.
Also, I’m required to inform you that Brahe had a fake nose. He lost his in a duel, but had a brass replacement made.
In 1807, Friedrich Bessel was the first astronomer to measure the distance to a nearby star 61 Cygni. He used the technique of parallax, by measuring the angle to the star when the Earth was on one side of the Sun, and then measuring it again 6 months later when the Earth was on the other side.
With parallax technique, astronomers observe object at opposite ends of Earth’s orbit around the Sun to precisely measure its distance. Credit: Alexandra Angelich, NRAO/AUI/NSF.
Over the course of this period, this relatively closer star moves slightly back and forth against the more distant background of the galaxy.
And over the next two centuries, other astronomers further refined this technique, getting better and better at figuring out the distance and motions of stars.
But to really track the positions and motions of stars, we needed to go to space. In 1989, the European Space Agency launched their Hipparcos mission, named after the Greek astronomer we talked about earlier. Its job was to measure the position and motion of the nearby stars in the Milky Way. Over the course of its mission, Hipparcos accurately measured 118,000 stars, and provided rough calculations for another 2 million stars.
That was useful, and astronomers have relied on it ever since, but something better has arrived, and its name is Gaia.
Launched in December 2013, the European Space Agency’s Gaia in is in the process of mapping out a billion stars in the Milky Way. That’s billion, with a B, and accounts for about 1% of the stars in the galaxy. The spacecraft will track the motion of 150 million stars, telling us where everything is going over time. It will be a mind bending accomplishment. Hipparchus would be proud.
With the most precise measurements, taken year after year, the motions of the stars can indeed be calculated. Although they’re not enough to see with the unaided eye, over thousands and tens of thousands of years, the positions of the stars change dramatically in the sky.
The familiar stars in the Big Dipper, for example, look how they do today. But if you go forward or backward in time, the positions of the stars look very different, and eventually completely unrecognizable.
When a star is moving sideways across the sky, astronomers call this “proper motion”. The speed a star moves is typically about 0.1 arc second per year. This is almost imperceptible, but over the course of 2000 years, for example, a typical star would have moved across the sky by about half a degree, or the width of the Moon in the sky.
A 20 year animation showing the proper motion of Barnard’s Star. Credit: Steve Quirk, images in the Public Domain.
The star with the fastest proper motion that we know of is Barnard’s star, zipping through the sky at 10.25 arcseconds a year. In that same 2000 year period, it would have moved 5.5 degrees, or about 11 times the width of your hand. Very fast.
When a star is moving toward or away from us, astronomers call that radial velocity. They measure this by calculating the doppler shift. The light from stars moving towards us is shifted towards the blue side of the spectrum, while stars moving away from us are red-shifted.
Between the proper motion and redshift, you can get a precise calculation for the exact path a star is moving in the sky.
Credit: ESA/ATG medialab
We know, for example, that the dwarf star Hipparcos 85605 is moving rapidly towards us. It’s 16 light-years away right now, but in the next few hundred thousand years, it’s going to get as close as .13 light-years away, or about 8,200 times the distance from the Earth to the Sun. This won’t cause us any direct effect, but the gravitational interaction from the star could kick a bunch of comets out of the Oort cloud and send them down towards the inner Solar System.
The motions of the stars is fairly gentle, jostling through gravitational interactions as they orbit around the center of the Milky Way. But there are other, more catastrophic events that can make stars move much more quickly through space.
When a binary pair of stars gets too close to the supermassive black hole at the center of the Milky Way, one can be consumed by the black hole. The other now has the velocity, without the added mass of its companion. This gives it a high-velocity kick. About once every 100,000 years, a star is kicked right out of the Milky Way from the galactic center.
A rogue star being kicked out of a galaxy. Credit: NASA, ESA, and G. Bacon (STScI)
Another situation can happen where a smaller star is orbiting around a supermassive companion. Over time, the massive star bloats up as supergiant and then detonates as a supernova. Like a stone released from a sling, the smaller star is no longer held in place by gravity, and it hurtles out into space at incredible speeds.
Astronomers have detected these hypervelocity stars moving at 1.1 million kilometers per hour relative to the center of the Milky Way.
All of the methods of stellar motion that I talked about so far are natural. But can you imagine a future civilization that becomes so powerful it could move the stars themselves?
In 1987, the Russian astrophysicist Leonid Shkadov presented a technique that could move a star over vast lengths of time. By building a huge mirror and positioning it on one side of a star, the star itself could act like a thruster.
An example of a stellar engine using a mirror and a Dyson Swarm. Credit: Vedexent at English Wikipedia (CC BY-SA 3.0)
Photons from the star would reflect off the mirror, imparting momentum like a solar sail. The mirror itself would be massive enough that its gravity would attract the star, but the light pressure from the star would keep it from falling in. This would create a slow but steady pressure on the other side of the star, accelerating it in whatever direction the civilization wanted.
Over the course of a few billion years, a star could be relocated pretty much anywhere a civilization wanted within its host galaxy.
This would be a true Type III Civilization. A vast empire with such power and capability that they can rearrange the stars in their entire galaxy into a configuration that they find more useful. Maybe they arrange all the stars into a vast sphere, or some kind of geometric object, to minimize transit and communication times. Or maybe it makes more sense to push them all into a clean flat disk.
Amazingly, astronomers have actually gone looking for galaxies like this. In theory, a galaxy under control by a Type III Civilization should be obvious by the wavelength of light they give off. But so far, none have turned up. It’s all normal, natural galaxies as far as we can see in all directions.
For our short lifetimes, it appears as if the sky is frozen. The stars remain in their exact positions forever, but if you could speed up time, you’d see that everything is in motion, all the time, with stars moving back and forth, like airplanes across the sky. You just need to be patient to see it.
