Researchers have captured the best-ever image of Sagittarius A*, the supermassive black hole at the center of our Milky Way galaxy, by using a new computer model to see through the haze of plasma surrounding the cosmic monster.
“The galactic centre is full of matter around the black hole, which acts like frosted glass that we have to look through to see the black hole,” Max Planck Institute researcher Eduardo Ros said of the discovery.
The fresh image of the black hole, which is twice the resolution of the previous best one, is described in a new paper in The Astrophysical Journal.
Researchers used 13 powerful telescopes around the world to capture the image and have been teasing its release since earlier in January.
According to reports, strophysicists had assumed that such a black hole would show a gigantic jet of matter and radiation.
Surprisingly, they didn’t find such a jet coming out of the Milky Way’s monstrous black hole. Either it doesn’t have one — or they can’t see it because it’s pointed directly at us.
Even if that were the case, Ros cautioned, it’s not cause for alarm.
“If anything is there, it will be a length that is 1,000 times less than the distance to us,” Ros said. “There is no danger at all – we should not fear the supermassive black hole.”
After a decade of bewilderment, astronomers have pinpointed the source of a mysterious blast of radio waves coming from deep outside the Milky Way: a dwarf galaxy located 3 billion light years from Earth.
It’s a remarkable first in the study of what has been a tremendous astronomical puzzle.
Scientists still don’t know what causes these deep space pulses, but locating the galaxy that spawned one brings us closer to figuring out where they come from.
First discovered in 2007, only 18 of these phenomena have ever been detected.
They’re called fast radio bursts, or FRBs, because they occur for just milliseconds; their fleeting nature makes it tough to catch one in action, and even tougher to figure out the exact spot in the sky they’re coming from.
But astronomers got lucky when they found a particular burst known as FRB 121102: it is the only one known to repeat, meaning multiple radio bursts have been detected coming from the same location in the sky.
That makes it easier for scientists to catch again, Shami Chatterjee, an astronomer at Cornell University who discovered the repetition says.
That discovery gave Chatterjee the idea to continually observe FRB 121102 with a huge network of radio telescopes.
And sure enough, he and his team were able to get high-resolution images of multiple bursts after many hours of observation, allowing them to track down the source of FRB 121102.
Their work is detailed today in three studies published in Nature and The Astrophysical Journal Letters.
The mystery of fast radio bursts
When FRBs were first discovered, there was debate over whether or not these signals were actually coming from space at all. Astronomers wondered if they were just bizarre interference of some kind.
But after a closer look, researchers realized FRBs are unique. Typically, a burst of radio waves will have different wave frequencies occurring at once, but FRBs have frequencies that are spread out.
The highest frequencies of each FRB arrive slightly earlier at Earth while the lowest frequencies arrive slightly later.
It’s a sign that the these FRBs are weary travelers, having journeyed through a lot of interstellar gas and plasma that’s mucking up their signals.
And FRB signals are so mucked up that astronomers are convinced they’re coming from outside the Milky Way Galaxy. But that creates another problem: these bursts must come from a super bright source.
“Like absolutely, incredibly bright,” says Chatterjee. Experts have come up with dozens of theories, such as the cataclysmic collision of neutron stars or a black hole tearing itself apart.
But no one has agreed on a single explanation.
Then the discovery of FRB 121102 changed everything. Because of its repeating nature, astronomers know that its source can’t be anything explosive or an object being destroyed.
“Something like that could not repeat again at the same place at the same distance,” says Chatterjee. “So that basically put the end to a huge swath of models.”
Maybe more than one thing is capable of creating FRBs — and that’s why there hasn’t been a single explanation. But the only way to know for sure was to find the host galaxy.
Another possibility is that the FRB is coming from a type of dense neutron star with an incredibly strong magnetic field, called a magnetar.
Astronomers have discovered magnetars in our galaxy that produce bright radio pulses, but nothing as bright as FRB 121101.
So something would have to be amplifying the pulses, like the way a magnifying glass focuses a beam of light on ants.
That may mean blobs of plasma are lining up just right to focus the radio waves on Earth, making them extra bright, says Chatterjee. “This is very plausible,” he says. “We’re not invoking any radical new physics.”
In late 2017, scientists with the Event Horizon Telescope – an international collaboration that’s created a virtual Earth-sized telescope, with the goal of capturing the first direct image of a black hole – reported on a the long-awaited shipment of hard disk drives from the South Pole.
They said they were busily analyzing the data on these drives, which is expected to be a key component in giving us the first-ever direct image of a black hole sometime in 2019.
As most of us know, black holes are truly black. That is, they are regions containing so much mass squeezed into so little space – regions of such powerful gravity – that no information or light or anything can escape, even if moving at the fastest speed known to exist in our universe, the speed of light.
Astronomers with the Event Horizon Telescope aren’t aiming to capture the black nothingness of a black hole itself (that’s not possible), but instead a black hole’s event horizon, the sphere-like point-of-no-return surrounding a black hole.
Which black hole then? Naturally, they’ll want to image the black hole that appears biggest from Earth.
The first logical choice is Sagittarius A* – pronounced Sagittarius A-star – a 4-million-solar-mass black hole located at the center of our home galaxy, the Milky Way.
This supermassive black hole is about 27,000 light-years from Earth.
The secondary target of the Event Horizon Telescope is much, much farther away, some 50-60 million light-years from Earth.
It’s the supermassive black hole at the center of M87: the largest galaxy in our home galaxy cluster, the Virgo cluster.
How can it appear big to us, at such a great distance away? It contains over 6 billion solar masses. This black hole is so big it could swallow our solar system whole.
That question is not as simple as it may sound. You might think that space appears dark at night because that is when our side of Earth faces away from the Sun as our planet rotates on its axis every 24 hours.
But what about all those other far away suns that appear as stars in the night sky? Our own Milky Way galaxy contains over 200 billion stars, and the entire universe probably contains over 100 billion galaxies.
You might suppose that that many stars would light up the night like daytime!
Until the 20th century, astronomers didn’t think it was even possible to count all the stars in the universe. They thought the universe went on forever. In other words, they thought the universe was infinite.
Besides being very hard to imagine, the trouble with an infinite universe is that no matter where you look in the
night sky, you should see a star.
Stars should overlap each other in the sky like tree trunks in the middle of a very thick forest.
But, if this were the case, the sky would be blazing with light. This problem greatly troubled astronomers and became known as “Olbers’ Paradox.” A paradox is a statement that seems to disagree with itself.
To try to explain the paradox, some 19th century scientists thought that dust clouds between the stars must be absorbing a lot of the starlight so it wouldn’t shine through to us.
But later scientists realized that the dust itself would absorb so much energy from the starlight that eventually it would glow as hot and bright as the stars themselves.
Astronomers now realize that the universe is not infinite. A finite universe—that is, a universe of limited size—even one with trillions and trillions of stars, just wouldn’t have enough stars to light up all of space.
Although the idea of a finite universe explains why Earth’s sky is dark at night, other causes work to make it even darker.
Not only is the universe finite in size, it is also finite in age. That is, it had a beginning, just as you and I did.
The universe was born about 15 billion years ago in a fantastic explosion called the Big Bang. It began at a single point and has been expanding ever since.
Because the universe is still expanding, the distant stars and galaxies are getting farther away all the time. Although nothing travels faster than light, it still takes time for light to cross any distance.
So, when astronomers look at a galaxy a million light years away, they are seeing the galaxy as it looked a million years ago.
The light that leaves that galaxy today will have much farther to travel to our eyes than the light that left it a million years ago or even one year ago, because the distance between that galaxy and us constantly increases.
That means the amount of light energy reaching us from distant stars dwindles all the time. And the farther away the star, the less bright it will look to us.
The universe, both finite in size and finite in age, is full of wonderful sights.
Night by night, star by star, astronomers are edging ever closer to learning just how crowded our universe really is—or at least our galaxy, anyway.
A quarter century after the first exoplanets were found orbiting other stars, statistics from the thousands now known have revealed that, on average, each and every stellar denizen of the Milky Way must be accompanied by at least one world.
Look long and hard enough for a planet around any given star in our galaxy and you are practically guaranteed to find something sooner or later.
But even a crowded universe can be a lonely place. Our planet-rich Milky Way may prove to be life-poor. Of all the galaxy’s known worlds, only a figurative handful resemble Earth in size and orbit.
Each occupying a nebulous “Goldilocks” region of just-rightness—a fairy-tale-simple ideal in which a world is neither too big nor too small, neither too hot nor too cold, to sustain liquid water and life on its surface.
Instead, most of the Milky Way’s planets are worlds theorists failed to predict and have yet to fit comfortably in any conception of habitability: “super-Earths” bigger than our familiar planet but smaller than Neptune.
No super-Earths twirl around our sun for solar system–bound scientists to directly study, making it that much harder to know whether any elsewhere are Goldilocks worlds—or, for that matter, whether any one-size-fits-all metric of habitability is hopelessly naive.
A Frozen Super-Earth?
“If you live in a city of millions of people, you are not interested in meeting every one of them—but maybe you want to meet your immediate neighbors,” says lead author Ignasi Ribas, an astronomer at the Institute of Space Studies of Catalonia in Spain.
“This is what we are doing for the planetary systems of the stars that surround us. Otherwise we cannot answer the big questions. How does our solar system and our Earth fit in with the rest of the galaxy?
“Are there other habitable or inhabited planets? Barnard’s Star b is not giving us those answers just yet, but it is telling us part of the story we need to know.”
Located in the constellation of Ophiuchus, Barnard’s Star is so dim in visible light that it cannot be seen with unaided eyes.
Yet it has been a favorite of astronomers since 1916, when measurements revealed its apparent motion across the sky was greater than that of any other star relative to our sun.
A sign of its extremely close cosmic proximity. The star’s nearness to us is only temporary—within tens of thousands of years, its trajectory will have swept it out of our solar system’s list of top five closest stars.
According to Ribas and his colleagues, the candidate planet is at least three times heavier than our own, and circles its star in a 233-day orbit.
That would put it in the torrid orbital vicinity of Venus around our yellow sun, but Barnard’s Star is a comparatively pint-size and dim red dwarf star.
This means its newfound companion is near the “snow line,” the boundary beyond which water almost exclusively exists as frozen ice—a region around other stars thought to be chock-full of planets, but that astronomers have only just begun to probe for small worlds.
Alternatively, the planet might be covered by a thick, insulating blanket of hydrogen leftover from its birth in a spinning disk of gas and dust around its star.
Although hydrogen on smaller, hotter worlds would dissipate into space, super-Earths in frigid orbits might manage to hang on to enough of the gas to build up a massive planet-warming greenhouse effect—a possibility that throws Earth-centric Goldilocks ideas into tumult.
If this mechanism operates on Barnard’s Star b or other cold super-Earths, “our dreams that every star may have a habitable planet could well come true,” says Sara Seager, a planet-hunting astrophysicist at Massachusetts Institute of Technology who was not involved with Ribas’s study.
Just over three years ago, physicists working in Antarctica announced they’d detected the first evidence of mysterious subatomic particles, known as neutrinos, coming from outside our galaxy.
It was a huge moment for astrophysics, but since then, no one’s quite been able to figure out where those particles are coming from, and what’s sending them hurtling our way.
Until now, that is – a team of astronomers has just identified the possible source of one these extragalactic visitors, and it appears that it started its journey to us nearly 10 billion years ago, when a massive explosion erupted in a galaxy far, far away.
Let’s step back for a second here though and explain why this is a big deal. Neutrinos are arguably the weirdest of the fundamental subatomic particles.
They don’t have any mass, they’re incredibly fast, and they’re pretty much invisible, because they hardly ever interact with matter.
Like tiny ghosts, billions of neutrinos per second are constantly flowing through us, and we never even know about it.
In order to detect them, researchers have step up extravagant labs, like the IceCube Neutrino Observatory at the South Pole, where they wait patiently to capture glimpses of neutrinos streaking through the planet, and measure how energetic they are, to try to work out where they came from.
Usually that source is radioactive decay here on Earth or inside the Sun, or maybe from the black hole at the centre of our galaxy.
But in 2013, the IceCube researchers announced they’d detected a couple of neutrinos so unimaginably energetic, they knew they must have come from outside our galaxy.
These neutrinos were named ‘Bert’ and ‘Ernie‘ (seriously) and they were the first evidence of extragalactic neutrinos.
Their discovery was followed by the detection of a couple of dozen more, slightly less energetic, extragalactic neutrinos over the coming months.
Then at the end of 2012, they spotted ‘Big Bird‘.
At the time it was the most energetic neutrino ever detected, with energy exceeding 2 quadrillion electron volts – that’s more than a million million times greater than the energy of a dental X-ray.
Not bad for a massless ghost particle.
Since then, teams across the world have been working to figure out where the hell this anomaly had come from. And now we might finally have a suspect.
This year, astronomers stumbled across a fascinating finding: Thousands of black holes likely exist near the center of our galaxy.
The X-ray images that enabled this discovery weren’t from some state-of-the-art new telescope. Nor were they even recently taken – some of the data was collected nearly 20 years ago.
No, the researchers discovered the black holes by digging through old, long-archived data.
Discoveries like this will only become more common, as the era of “big data” changes how science is done.
The evolution of astronomy
Sixty years ago, the typical astronomer worked largely alone or in a small team. They likely had access to a respectably large ground-based optical telescope at their home institution.
Their observations were largely confined to optical wavelengths – more or less what the eye can see.
That meant they missed signals from a host of astrophysical sources, which can emit non-visible radiation from very low-frequency radio all the way up to high-energy gamma rays.
For the most part, if you wanted to do astronomy, you had to be an academic or eccentric rich person with access to a good telescope.
Astronomers are gathering an exponentially greater amount of data every day – so much that it will take years to uncover all the hidden signals buried in the archives.
Old data was stored in the form of photographic plates or published catalogs. But accessing archives from other observatories could be difficult – and it was virtually impossible for amateur astronomers.
Unlocking new science
The data deluge will make astronomy become a more collaborative and open science than ever before. Thanks to internet archives, robust learning communities and new outreach initiatives, citizens can now participate in science.
For example, with the computer program [email protected], anyone can use their computer’s idle time to help search for gravitational waves from colliding black holes.
Most of us have looked up at the night sky and wondered how far away the stars are or in what direction they are moving.
The truth is, scientists don’t know the exact positions or velocities of the vast majority of the stars in the Milky Way.
But now a new tranche of data from the European Space Agency’s Gaia satellite, aiming to map stars in our galaxy in unprecedented detail, has come in to shed light on the issue.
The Gaia Archive opened on April 25, making public Gaia’s second data release to everyone.
To quote the character Dave Bowman in the sci-fi classic 2001: A Space Odyssey: “It’s full of stars”. In fact, it contains data on the distances to more than 1.3 billion stars.
The Gaia satellite was launched in 2013 and has been scanning the sky with its two telescopes continuously ever since, with the aim of deciphering how our Milky Way galaxy formed and evolved.
To do this, it is measuring something called parallax. If you hold a finger at arms length and look at it with one eye and then the other, your finger appears to shift position compared to the background.
The angular change is called parallax.
Being in space allows Gaia to see similar tiny shifts in star positions. Observations at different locations six months apart (half way of its orbit around the Earth) are akin to looking at your finger with one eye and then the other.
When you know the parallax as well as the distance from Gaia to the sun (or the distance from your nose to your eye), you can use simple trigonometry to work out the distance to each star (or your finger).
Gaia also sees stars move in the plane of the sky over time. These units of “angle per time” can be converted to a physical unit of speed (for example kilometres per second) if we know the distance to the stars.
However, to know how a star is moving in three dimensions in space requires that we also measure the speed perpendicular to the sky along the line-of-sight. This requires a galactic speed camera!
A normal radar speed camera uses the Doppler effect – the stretching or squashing of waves because of motion – by measuring the change in the radio frequency from signals bounced off cars to measure their speed.
Similarly, Gaia measures the change in frequency in the light from stars to check their speed. The star light is bluer if the star is moving towards us or redder if the star is moving away from us. This is called radial velocity.
Gaia’s first data release in 2016 published the distances of around two million stars but did not include any radial velocities.
However we already knew the radial velocity of less than 400,000 of these stars – measured from the ground by many different surveys.
Gaia’s second data release includes information on sky positions and brightness for nearly 1.7 billion stars and more than seven million radial velocities.
Not only does this make Gaia the largest radial velocity survey ever – it increases the number of stars with accurate 3D space velocities by a factor of 18.
A series of Gaia science demonstration papers have also been published alongside the star catalogue. I was involved in the research behind one of these papers, constructing the most detailed map ever of 3D space velocities to date.
The next data release by Gaia will be in 2020. This is expected to boost the numbers of stars with known radial velocities from seven million today to around 30m – keeping our team busy for several years yet.
Galaxies are a fundamental part of the 13.7 billion-year-old universe. Understanding how a system as complex and striking as our own Milky Way galaxy formed after the Big Bang is one of the great themes of modern astronomy.
Our research, published today in Nature Astronomy, has identified a surprising connection between the age of a galaxy and its three-dimensional shape.
As galaxies get older they get rounder, and fall victim to the middle-aged spread that catches many of us humans here on Earth.
We’ve known for a long time that shape and age are linked in very extreme galaxies – that is, very flat ones and very round ones.
But this is the first time we have shown this is true for all kinds of galaxies – all shapes, all ages, all masses.
Unveiling the true face of a galaxy
In this study we calculated both the age and shape of galaxies using different techniques.
Assigning an age to a galaxy is tricky. They don’t have a single birth date for when they suddenly popped into existence.
We assessed the average age of the stars in a galaxy as a measure of the galaxy’s age. Young galaxies have a large fraction of recently formed hot blue stars, whereas old galaxies mostly contain colder red stars formed shortly after the Big Bang.
Spectroscopy — splitting the light from a galaxy into many different colours — allows us to measure the average age of stars in a galaxy.
This technique gives a much higher precision than simply using blue or red images as is typically done.
To measure a galaxy’s true three-dimensional shape and ellipticity, you have to measure how its stars move around.
Ellipticity is simply a measure of how squashed a galaxy is with respect to a perfect sphere. An ellipticity of zero means a galaxy is a perfect sphere like a soccer ball.
But as the measured ellipticity increases from zero towards one, the galaxy becomes more and more squashed – from a roundish pumpkin shape to a thin disk like a pancake.
We see galaxies as two-dimensional images projected onto the sky, but that doesn’t tell us what they really look like in three dimensions.
If we can also measure how the stars in a galaxy are moving we can infer their true, three-dimensional shape.
Spectroscopy lets us do this via the Doppler effect. We can measure shifts in the wavelength of light emitted by stars, which depend on whether those stars are moving towards us or away from us, and so measure their motions.
We did this using SAMI, the Sydney-Australian-Astronomical-Observatory Multi-object Integral-Field Spectrograph, on the 3.9-metre Anglo-Australian Telescope at Siding Spring Observatory.
The SAMI instrument provides 13 optical fibre units that can “dissect” galaxies using spectroscopy, providing unique 3D data.
Over the past couple of years, the SAMI Galaxy Survey team has gathered 3D measurements for more than a thousand galaxies of all kinds, and with a hundred-fold range in mass.
Closer to home
If we look at our own Milky Way galaxy, which is more than 10 billion years old, we can see examples of this story.
The youngest part of the Milky Way, where stars are still being formed, is the thin disk, which has a very squashed, pancake-like shape.
The Milky Way also contains rounder and older components, a thick disk and a bulge, but their origin is still mostly unknown.
We know that eventually the Milky Way will merge with our galactic neighbour, the Andromeda galaxy. Predictions are that this will result in a very round, very old giant elliptical galaxy.
So, by studying the processes that shape other nearby galaxies, we can learn a lot about the past, and the fate of our own.