Milky Way

Research & Innovation

Canadian Institute for Theoretical Astrophysics

University of Toronto researcher Amanda Cook has found a way to use bright signals coming from across the universe to weigh the atmosphere of the Milky Way galaxy.

The radio signals she used come from the astronomical phenomenon known as fast radio bursts (FRBs) – enigmatic celestial objects that generate brief flashes of radio waves and are considered one of the biggest mysteries in astronomy.

Since an FRB simultaneously generates both high frequency radio waves (the equivalent of blue light) and low frequency radio waves (the equivalent of redlight), the different colours of radio waves might be expected to arrive at a telescope at the same time. But that’s not what happens. As an FRB passes through gas, it slows down – more so for the high frequencies than the low frequencies. The result is a delay between the different frequencies or colours reaching our telescope, effectively smearing the radio burst’s signal out in time.

Astronomers like Cook call this smearing “dispersion” and are able to use it as a tool to detect otherwise invisible gas throughout the cosmos.

“Using smearing to study the universe is like using your home heating bill to work out what the weather must have been like over the winter,” says Cook, who is a PhD candidate in the David A. Dunlap department of astronomy and astrophysics, and the Dunlap Institute for Astronomy & Astrophysics, in the Faculty of Arts & Science. “In the same way that your heating bill tells you whether it was a harsh winter or a mild winter – but not what the temperature was like on any individual date – the smearing that we see allows us to infer the total amount of material that the FRB signal has encountered on its journey from the FRB to Earth. It just can’t tell us how that material was distributed along the way.”

“The key thing is that regardless of how gas in front of the FRB is distributed, an FRB signal that is smeared more by the time it reaches our telescopes must be produced by an FRB that is farther away in the same way that an expensive heating bill must have meant a cold winter overall.”

An illustration of a radio signal from a fast radio burst as it moves toward telescopes on Earth (image courtesy of J. Josephides/Swinburne University of Technology, with minor edits from the Dunlap Institute)

In this case, Cook used the dispersion method to measure how much gas is present in the Milky Way’s halo – an “atmosphere” of the Milky Way that extends outwards by around a half a million light-years in all directions.

Using FRB signals collected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope, Cook and her team discovered that the Milky Way’s halo contains much less gas than previous models had predicted. The results were published in the Astrophysical Journal in a study titled, “An FRB Sent Me a DM.”

Though there had been earlier studies applying related techniques, this is the first time that the halo’s gas has been measured using a large uniform sample of FRBs – thanks to the CHIME telescope.

The team used FRB signals at different distances from Earth to get the result. Cook likens this approach to trying to work out the average driving distance from different Canadian border crossings to Toronto by having friends from different American states drive to Toronto, telling you only the total distance they drove. The information from your Texan friend is not going to be particularly useful, but the experience from your Michigan and New York friends may be far more insightful. And if you have friends that live right on the border, in Buffalo or Detroit, then their answers will pretty much give you the information you need.

Cook and her supervisor, Professor Bryan Gaensler, have been working on this research since she was a first-year graduate student. “It ended up being a lot more difficult than we thought,” Cook says.

Difficult enough, that she, Gaensler and their colleagues actually stepped outside of conventional astronomical models. They turned to researchers in an entirely different field – statistics – and asked those colleagues for a new set of methods to apply to their approach.

“This is an exciting new way of studying our Milky Way,” says Gaensler, who is also an author on the publication. “We’re still trying to figure out what fast radio bursts actually are, but in the meantime we can use them as searchlights to study things much closer to home.”

Cook and Gaensler note that FRB signals could be used to study the structure of everything that the FRB signal passes through on its long journey, including the material between galaxies, the halos of other galaxies and the gas inside of galaxies.

Meanwhile, many more FRB discoveries are anticipated. With even more data, Cook and her team hope to create a 3D map of the Milky Way halo. “Each FRB gives us a measurement of the Milky Way halo in one direction, so as we continue to collect them, we can build up a detailed picture,” Cook says.

Beyond that, she notes that these clues contribute to our understanding of the early universe.

“Improving our knowledge of the Milky Way halo helps us learn about the formation of our galaxy as a whole.”

'A very big deal': Astrophysicist Ue-Li Pen on the first image of the Milky Way's supermassive black hole

Christopher.Sorensen — Fri, 13 May 2022 14:03:34 +0000

'A very big deal': Astrophysicist Ue-Li Pen on the first image of the Milky Way's supermassive black hole

Christopher.Sorensen Fri, 05/13/2022 - 10:03

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The first image of Sagittarius A*, or Sgr A*, the supermassive black hole at the centre of our Milky Way galaxy (Image by Event Horizon Telescope Collaboration)

Josslyn Johnstone

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Canadian Institute for Theoretical Astrophysics

Astronomers this week revealed the first image of the supermassive black hole at the heart of a galaxy not so far, far away – our home galaxy, the Milky Way.

Scientists had previously observed stars orbiting around something invisible, compact and very massive at the centre of the Milky Way. Known as Sagittarius A*, or Sgr A*, the object was strongly believed to be a black hole.

The Event Horizon Telescope (EHT) collaboration is the international research team behind this groundbreaking achievement, involving over 300 scientists from 80 institutions around the globe. The EHT team linked together eight existing radio observatories across the planet to form a single Earth-sized virtual telescope to provide the first direct visual evidence of Sgr A*. The telescope is named after the event horizon, the boundary of the black hole beyond which no light can escape.

It is just the second image of a black hole to be captured after EHT revealed the first-ever image of M87* in the distant Messier 87 galaxy in 2019.

Canadian Institute for Theoretical Astrophysics (CITA) Professor Ue-Li Pen is a collaborating scientist on the EHT project. Currently based in Taipei, Taiwan, Pen is also the director of the Academia Sinica Institute for Astronomy and Astrophysics, one of the key institutes leading the experiment, and an associate faculty member at the Dunlap Institute for Astronomy & Astrophysics in the University of Toronto’s Faculty of Arts & Science.

He recently shared his insights with writer Josslyn Johnstone on the discovery, the results of which were published May 12 in a special issue of The Astrophysical Journal Letters and showcased at simultaneous press conferences held around the world.

What makes this new, second image of a black hole so important?

Scientifically, this discovery is a very big deal because Sgr A* is more than a thousand times closer than M87* – about 27,000 light-years away versus 53 million. We can study it in much finer detail and can do so much more with it than with an object that’s very far away and barely measurable.

This black hole being in our home galaxy – as close to home as you can get when talking about outer space, anyway – makes it that much more fascinating and immediate. I liken it to this: It’s one thing to discover an ancient dinosaur bone, and another entirely to see a live dinosaur right in your backyard.

It is an astounding collective achievement where researchers collaborated across continents, countries, cultures and time zones to make it happen. It shows what amazing things can happen when people work together.

If this black hole is so much closer, why did researchers first capture an image of M87*?

When seen from Earth, the angular size of both black holes is similar. However, M87* is not only much further away, but it is more than a thousand times bigger and more massive than Sgr A*. It's like the moon and the sun – they appear roughly the same size from Earth, but the sun is much larger.

It is hard to make an image instantly because we don't have all the information – the missing pixels, so to speak. Ideally, you would cover the whole Earth with telescopes but, of course, we don't have that many. We had eight telescopes capturing data at any given time. So, to fill in the gaps on the planet where there are no telescopes, where there is no data, we wait for the Earth to rotate.

Because the black hole that is farther away is much bigger, it rotates more slowly. That makes is easier to scan across the black hole and make one image. The black hole in the centre of our own galaxy is much smaller and varying intrinsically – meaning, instead of scanning a static snapshot of an object, you are trying to reconstruct something that is constantly changing as you look at it. It's tricky to disentangle what is due to the earth rotating or the black hole rotating, because they are both changing. That's why it took so many years longer to image Sgr A*, even though the data for both black holes was collected in the same 2017 period.

Is this why there is such a visual difference between the Sgr A* and M87* images?

Right – unlike the 2019 M87* image, which was one clear picture of a black hole, in this case it is a series of images that are reconstructions of what Sgr A* might look like. It is not as distinct, where you can say, “This is it.” Instead, it is a Platonic master image with variations of what it could look like: “It may look like this, or it may look like that.”

It’s like taking a picture of a fast-moving object, like a baseball, on an SLR camera – the ball is moving at the same time as the exposure, so you end up with a distorted image.

What questions are we hoping to answer with this new image?

In a sense, by capturing that first image of the black hole that was farther away, we still had the same questions … then had even more. I think the image of Sgr A* holds all the answers, or at least a lot of them, because we’re able to get that much closer to see what’s going on. We already knew the black hole was there. Now we have a hope of understanding why black holes exist and how they form by studying the surrounding environment. My primary research interests are the compact objects near the black hole called pulsars, so I am looking to measure pulsars in the same dataset.

Now that we have the image, what are the researchers working on next?

The next analysis will be incredibly scientifically valuable, as it will measure the polarization of the emission. Think of polarized sunglasses, where light comes in two polarizations that you can study: reflected sunlight and the resulting glare. By rotating your polarization filter, you can understand what is reflected and what is not. This is similar for the black hole. With polarization, you can study the nature of the radiation emission. Whereas right now, it's a bit unclear what we're looking at. With polarization I think it will be much clearer.

Astronomers focus robotic eyes on the Milky Way, our cosmic home

Christopher.Sorensen — Fri, 21 Jan 2022 00:22:28 +0000

Astronomers focus robotic eyes on the Milky Way, our cosmic home

Christopher.Sorensen Thu, 01/20/2022 - 19:22

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The Sloan Foundation 2.5-metre telescope at Apache Point Observatory in New Mexico is one of two sites to use a new Focal Plane System to study the Milky Way (photo courtesy of Fermilab Visual Media Services)

Chris Sasaki

Sean Bettam

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Global Lens

Astronomy & Astrophysics

Thanks to a breakthrough robotic innovation, an international collaboration that includes the University of Toronto has advanced the Sloan Digital Sky Survey (SDSS), a 20-year-long research project that has been investigating the structure and evolution of our cosmic home, the Milky Way galaxy.

A new Focal Plane System (FPS) is at the heart of the fifth phase of the project, dubbed SDSS-V. The system replaces a time-consuming, hands-on approach to making simultaneous observations of hundreds of stars that required astronomers to manually plug hundreds of optical fibres into holes drilled into a metal plate in the focal plane of a telescope.

With this new innovation, the system’s 500 robotic positioner units replace human hands and precisely maneuver optical fibres into position in the telescope’s focal plane so that each can gather the light of a specific star within the target area.

“We are going from collecting a few thousand spectra per night to nearly 15 thousand,” says Juna Kollmeier, director of SDSS-V, the fifth phase of SDSS, and director of �Թϱ��’s Canadian Institute for Theoretical Astrophysics (CITA).

“It's a fantastic change in how we operate that will not only allow us to survey more objects, but to probe these systems over time, on timescales we couldn't access previously. This opens up a tremendous wealth of new science.”

In addition to Kollmeier, other �Թϱ�� astronomers involved in SDSS-V include Associate Professor Jo Bovy, Assistant Professor Maria Drout and Assistant Professor Ting Li – all of the David A. Dunlap department of astronomy and astrophysics in the Faculty of Arts & Science – and Ted Mackereth, a Banting-Dunlap-CITA post-doctoral fellow.

“I run massive calculations about the Milky Way galaxy,” says Mackereth. “At the end of the day, I want to test these ideas and SDSS-V will be a key way to do that.”

“SDSS has been an important testbed for some of the most exciting advances in machine learning,” adds Bovy, whose early work in previous phases of SDSS pioneered techniques for age-dating in the galaxy. “Using these techniques, we are able to get ages for millions of stars – something we didn't think was possible when SDSS began."

Drout, meanwhile, is one of the leaders of the Time Domain effort in SDSS-V. She and her collaborators will use the spectra statistically to probe the ways in which astrophysical objects change in time.

The Focal Plane System replaces a time-consuming, hands-on approach to making simultaneous observations of hundreds of stars (photo courtesy of SDSS-V)

The development of the new robotic FPS was a five-year effort by an international team, including Ohio State University’s Imaging Sciences Laboratory, the University of Washington, École Polytechnique Fédérale de Lausanne (EPFL) and the Carnegie Observatories in Pasadena.

The design teams overcame numerous challenges posed by the global pandemic by developing and constructing components wherever they were – some in their own garages and backyards – and shipping them elsewhere for further assembly. The robots were built in Switzerland and integrated into the main mechanical units in Columbus, Ohio.

Previous phases of SDSS observed nearly a million stars in our home galaxy using spectrographs – instruments capable of measuring a star’s light at different wavelengths. The resulting spectra reveal a remarkable amount of information about stars: their age, temperature, chemical composition, motion and more. SDSS-V will observe over five million stars.

There are two FPS units. One is in operation on the Sloan Foundation 2.5-metre telescope at Apache Point Observatory (APO) in New Mexico. A second unit is under construction and when complete, will operate on a telescope at the Las Campanas Observatory in northern Chile. (At the Las Campanas Observatory in 1987, �Թϱ�� astronomer Ian Shelton was one of the two observers to first see Supernova 1987A, an exploding star in the Milky Way galaxy’s companion galaxy, the Large Magellanic Cloud.)

The FPS will enable two of the three core science programs in SDSS-V: the Milky Way Mapper (MWM) and the Black Hole Mapper (BHM). Together, these projects will collect data from millions of objects spread across the sky, from stars in our own galactic backyard to unimaginably distant supermassive black holes.

The MWM will study our home galaxy in unprecedented detail. It will take advantage of our unique perspective within the Milky Way to create a high-resolution map of the galaxy’s stars and how they are moving.

The MWM will also measure masses, ages, chemical compositions, the presence of companions and a slew of other properties for vast samples of stars of all types – including hot massive stars, stars that are just forming and the white dwarfs that are dead remnants of stars like our Sun. It will also target tens of thousands of multi-star and planetary systems in order to understand how often multi-companion systems form and what determines how they are structured.

Looking farther afield, the BHM will study quasars, which are among the most luminous objects in the universe. Powered by material flowing into supermassive black holes at the centres of galaxies, quasars can be used as beacons to trace the growth of these titans over cosmic time. SDSS-V will collect data on more than 300,000 quasars to measure the masses of their black holes, understand the physics of how they gobble up matter and trace their growth over many billions of years.

These vast samples of strikingly different types of targets – millions of Milky Way Galaxy stars, hundreds of thousands of distant quasars – are among the key aspects that set SDSS-V apart from other surveys and are enabled by the new FPS system.

“This project has been truly collaborative, involving the contributions of scientists at more than 50 institutions from around the world,” says Kollmeier.

“We are thrilled to have reached this technological milestone despite being in the midst of a global pandemic and are excited to witness how this shift will enhance the work of the project.”

With files from SDSS

Researchers study Milky Way's 'feeding habits' in search of clues about its origins

Christopher.Sorensen — Tue, 11 Jan 2022 17:01:10 +0000

Researchers study Milky Way's 'feeding habits' in search of clues about its origins

Christopher.Sorensen Tue, 01/11/2022 - 12:01

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(Photo by Bill Ingalls/ NASA via Getty Images)

Meaghan MacSween

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Breaking Research

Global

Research & Innovation

Astronomers are one step closer to revealing the properties of dark matter enveloping our Milky Way galaxy thanks to a new map of 12 streams of stars orbiting within our galactic halo.

Understanding these star streams is very important for astronomers. As well as revealing the dark matter that holds the stars in their orbits, they also tell us about the formation history of the Milky Way, revealing that the galaxy has steadily grown over billions of years by shredding and consuming smaller stellar systems.

“We are seeing these streams being disrupted by the Milky Way’s gravitational pull, and eventually becoming part of the Milky Way,” said Ting Li, an assistant professor in the David A. Dunlap department of astronomy and astrophysics in the University of Toronto’ Faculty of Arts & Science.

Li is the lead author of a new paper (preprint available here) that has been accepted for publication in the American Astronomical Society’s Astrophysical Journal.

“This study gives us a snapshot of the Milky Way’s feeding habits, such as what kinds of smaller stellar systems it ‘eats,’ Li says. “As our galaxy is getting older, it is getting fatter.”

Li and her international team of collaborators initiated a dedicated program – the Southern Stellar Stream Spectroscopic Survey (S5) – to measure the properties of stellar streams: the shredded remains of neighbouring small galaxies and star clusters that are being torn apart by the Milky Way.

They are the first group of scientists to study such a rich collection of stellar streams, measuring the speeds of stars using the Anglo-Australian Telescope (AAT), a four-metre optical telescope in Australia. Li and her team used the Doppler shift of light to find out how fast individual stars are moving.

Unlike previous studies that have focused on one stream at a time, “S5 is dedicated to measuring as many streams as possible, which we can do very efficiently with the unique capabilities of the AAT,” says co-author Associate Professor Daniel Zucker of Macquarie University.

The properties of stellar streams reveal the presence of the invisible dark matter of the Milky Way.

“Think of a Christmas tree,” says co-author Professor Geraint Lewis of the University of Sydney. “On a dark night, we see the Christmas lights, but not the tree they are wrapped around. But the shape of the lights reveals the shape of the tree. It is the same with stellar streams – their orbits reveal the dark matter.”

A crucial ingredient for the success of S5 were observations from the European Gaia space mission. “Gaia provided us with exquisite measurements of positions and motions of stars – essential for identifying members of the stellar streams,” says Sergey Koposov, reader in observational astronomy in the University of Edinburgh and a co-author of the study.

As well as measuring their speeds, the astronomers can use these observations to work out the chemical compositions of the stars, telling us where they were born.

“Stellar streams can come either from disrupting galaxies or star clusters,” says Assistant Professor Alex Ji at the University of Chicago, a co-author on the study. "These two types of streams provide different insights into the nature of dark matter."

Li says the new observations are essential for determining how our Milky Way arose from the featureless universe after the Big Bang.

“For me, this is one of the most intriguing questions – a question about our ultimate origins,” Li says. “It is the reason why we founded S5 and built an international collaboration to address this”.

Li’s team plans to produce more measurements on stellar streams in the Milky Way. In the meantime, she is pleased with these results as a starting point.

“Over the next decade, there will be a lot of dedicated studies looking at stellar streams,” Li says. “We are trailblazers and pathfinders on this journey. It is going to be very exciting.”

X marks the spot at the centre of the Milky Way

lavende4 — Tue, 19 Jul 2016 12:52:23 +0000

X marks the spot at the centre of the Milky Way

lavende4 Tue, 07/19/2016 - 08:52

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Image of the Milky Way taken by the WISE space telescope. The circle is centred on the galaxy’s central region, while the inset shows an enhanced version of the same region with a clearer view of the X-shaped structure. (NASA/JPL-Caltech; D. Lang)

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Astronomy