University of Toronto student newspaper The Varsity recently published an article about our Star Talk with York University astronomer Paul Delany. Check it out at the link below:
Dr. Keith Vanderlinde discusses the evolution of radio telescope design
By Adam A. Lam
Why do radio telescopes look drastically different from optical telescopes? The answer, according to Dr. Keith Vanderlinde, is largely due to the large wavelengths of radio waves that these telescopes are designed to detect.
Dr. Vanderlinde—Associate Professor at the David A. Dunlap Department of Astronomy & Astrophysics and the Dunlap Institute—explored the design of radio telescopes and the future of radio astronomy at his October Star Talk with the Astronomy & Space Exploration Society.
Radio telescopes have typically appeared as massive structures of an antenna fixed to a parabolic dish. “There are two reasons that we make larger and larger telescopes,” he explained. “One is just to make a larger light bucket.” The larger surface area of the telescope’s dish, he continued, increases the sensitivity of the instrument.
The second reason stems from the challenge faced by radio telescopes in capturing images with high enough optical resolution. Resolution—the shortest length between two separate points in an image—is dependent on the colour (wavelength) of light (electromagnetic radiation) under observation, noted Dr. Vanderlinde.
The key measure of resolution, explained Dr. Vanderlinde, is the size of the “collecting area… in units of wavelengths.” Since radio waves have the longest wavelengths across the electromagnetic spectrum, he noted, radio telescopes must be built to large sizes for reasonable resolution.
This is why the Green Bank Telescope—a radio telescope 100 metres wide—still has a resolution around 20 times worse than the human eye, explained Dr. Vanderlinde. Historically, he added, the large size of radio telescopes have made the instruments vulnerable during natural disasters. Increased telescope size is also limited by prohibitive cost, he continued, along with physical space limitations.
In the 2000s, scientists and engineers began to address this challenge by designing aperture arrays. In this type of radio telescope, Dr. Vanderlinde explained, the integration of additional radio detectors boosts the instrument’s sensitivity as if the surface area of the telescope’s dish has increased. Contemporary radio telescopes, he noted, continue to harness the advantages of adding detectors in order to increase image resolution. This has made radio astronomy increasingly affordable.
“Previously, all the cost was in steel, [and] steel has been pretty stable in price,” he said. “Electronics are not stable in price; they drop drastically. If you can’t afford your telescope today, wait 18 months and it’ll cost half as much. If you can’t afford it, then wait another year and a half, and will be a quarter what it originally was.”
He continued: “Within a fairly small amount of time, you can afford to do almost anything. Because of this sort of digital revolution that we’re living in.”
—To learn more about the physics behind radio astronomy, along with the impact of consumer technology on radio astronomy, you can watch our recording of Dr. Vanderlinde’s Star Talk on the ASX Society’s YouTube Channel.
Dr. Abigail Crites discusses methods and goals in the process of improving observational tools
By Adam A. Lam
Working with an angle grinder and soldering, Dr. Abigail Crites has both in-depth practical and theoretical experience designing instruments that help researchers across the globe better understand what happened in the early universe, across the first billion years after the Big Bang.
Dr. Crites—Assistant Professor at the University of Toronto’s David A. Dunlap Department of Astronomy & Astrophysics and the Dunlap Institute and Visiting Associate at the California Institute of Technology—explained how innovation in astronomy instrumentation works at her September Star Talk with the Astronomy & Space Exploration Society.
To observe the universe, Dr. Crites explained, astronomers need to capture light—also known as electromagnetic radiation (EMR)—from across the universe. With visible light, scientists can make observations with optical telescopes. But EMR consists of frequencies outside the range of visible light—including ultraviolet light, X-rays, and radio waves.
Demonstrating this, Dr. Crites presented an online model of the universe called the Chromoscope, developed by educators at Cardiff University. Experimenting with the Chromoscope’s slider, she explained, presents different visualizations of the universe produced by various frequencies of EMR.
“If we just look at our galaxy or our universe, in the visible [light spectrum], we’re actually missing quite a bit of information,” she explained. Analyzing different frequencies, she continued, can uncover “very different structures” in the universe.
But how do astronomers capture this information? Dr. Crites explained that these observations are enabled by experts who develop the instruments to capture these data, who she described as the “builders” of astronomy.
These builders must ask and answer a series of questions, she continued, such as: “What do we specifically want to look at?… What technology [do] we need to do this? And what technology do we not have and need to develop?”
To answer the first question, Dr. Crites explained that astronomers often focus on a research question. Inspirations can include a blend of serendipitous discovery and knowledge of theory—which, she noted, led to the detection of the oldest light in the universe, known as the cosmic microwave background.
“Another way to decide what to look at is to… think about analogues in our solar system,” she explained. In the search for habitable exoplanets, she continued, astronomers can search for absorption lines in the electromagnetic spectrum that may indicate the existence of water on distant celestial bodies.
A third way to narrow down the wavelength and subject of searching the sky, she explained, “is to look at signals that might accompany other measurements in physics.” As an example, she noted: “when neutron stars merge, you actually get an electromagnetic signal as well as the gravitational wave signal.” Studying this electromagnetic signal, she continued, could help astronomers study this phenomenon.
To make these measurements, Dr. Crites continued, builders need a telescope to gather the light and a detector to convert the photons into measured voltages. A detector requires a component “to absorb the photons,” along with a part “to record the signal,” she explained. A basic example is a human observer, she reflected—with the eyes absorbing the photons and the brain capturing the signal. Modern detectors in astronomy, she explained, often rely on a silicon chip to absorb the photons, which “creates electrons that can be read out as electric signals by a computer.”
But for astronomers like Dr. Crites who study the history of the universe, the objects under study are so far away from Earth that the light they emit is faint. This has challenged builders to develop detectors with enough sensitivity to make these measurements.
Yet as Dr. Crites notes, the challenges are “worthwhile,” as the development of these instruments enable astronomers to probe physics at an ancient time when the universe was far less complex.
—To learn more about experimental astronomy during COVID-19, early inspirations that led Dr. Crites to astronomy research, and her advice on the importance of collaboration in astronomy research, you can watch our recording of Dr. Crites’s Star Talk on the ASX Society’s YouTube Channel.
Dr. Adam Hincks discusses the history and future of research on the origins of the universe
By: Adam A. Lam
Close to 14 billion years ago, the universe began with the Big Bang. A few hundred thousand years later, the oldest light in the universe accessible to us—named cosmic microwave background (CMB)—was emitted. This light, existing before the formation of the universe’s first stars, is a focus of astronomers who study the origins and evolution of the universe.
Dr. Adam Hincks, Assistant Professor at the University of Toronto with a joint appointment between the David A. Dunlap Department of Astronomy & Astrophysics and St. Michael’s College, is one such scientist.
“If you want [to study] the oldest light in the universe, you can’t look in optical wavelengths,” he said at his August Star Talk with the Astronomy & Space Exploration Society. “You can’t look using visible light that our eyes can see.”
Light, also known as electromagnetic radiation (EMR), travels at around 300,000 kilometres per second. But—as Dr. Hincks notes—EMR can be classified into different types, according to the frequency of the radiation. To visualize an example, he pictured the static of an “old analog television.” One per cent of that static you would see, he explained, is microwave radiation that originates from space.
This microwave radiation includes the CMB, which astronomers consider to be the oldest detectable EMR in the universe. At the time, Dr. Hincks explained, the universe consisted of hydrogen and helium in hot conditions at a nearly uniform density. Due to their heat, he continued, the gases emitted thermal radiation—known as CMB.
In 1964, astronomers Drs. Robert Woodrow Wilson and Arno Penzias discovered CMB with a radio telescope. “They found that no matter where they pointed this telescope at at the sky, they saw the same brightness everywhere in microwaves,” said Dr. Hincks. This reflects the uniform density of the hydrogen and helium that emitted the CMB, supporting the Big Bang Theory.
Closer to the present, in 1989, NASA launched a satellite named the Cosmic Background Explorer (COBE), which—as Dr. Hincks explained—can take precise measurements to study CMB. “It turns out that by looking at the precise details of [from observations of CMB],” said Dr. Hincks, “we can determine some pretty fundamental things about our universe.” These fundamentals the universe’s age, geometry, and composition—including the study of dark matter.
“About a quarter of the universe is made up of what we call dark matter,” he said. “This matter isn’t made up of the atoms that we know about: the atoms from the periodic table that you saw hanging in your chemistry classroom… We don’t know exactly what it is, but we know it’s there because we can very clearly see its gravitational effects.”
Dr. Hincks continued to explain the ambitious research projects undertaken by scientists and engineers across the globe to better study CMB. Highlights by Dr. Hincks include the active Atacama Cosmology Telescope, manufactured in Vancouver, Canada with the involvement of over a dozen institutions including the University of Toronto, along with the Simons Observatory currently in construction.
—To learn more about the importance, history, and future of CMB research, you can watch our recording of Dr. Hincks’s Star Talk on the ASX Society’s YouTube Channel.
By: Adam A. Lam
What is the mass of the Milky Way galaxy, and why is it important to investigate?
Dr. Gwen Eadie, an Assistant Professor jointly appointed between the University of Toronto’s David A. Dunlap Department of Astronomy & Astrophysics (DADAA) and its Department of Statistical Sciences (DoSS), spoke on these questions at the Astronomy and Space Exploration Society’s first Star Talk of the year on July 8. She discussed her research team’s investigations into the universe guided by statistical studies.
The structure of our universe
“To recreate this hierarchical structure in computer simulations of how the universe evolved, we’ve discovered that you have to include something called dark matter,” Dr. Eadie noted. Dark matter is a hypothetical, currently undetectable type of matter that has a gravitational effect on visible matter — but does not otherwise interact with it.
Astronomers believe that every galaxy in the universe, including the Milky Way, lives inside its own dark matter halo, continued Dr. Eadie. This structure of dark matter “represents a really large portion of the mass of the galaxy.”
By estimating the total mass of the Milky Way along with its total visible mass, Dr. Eadie explained, “you can subtract out the matter that we can see and figure out how much dark matter is there. And that might tell us something about the nature of dark matter itself.”
Challenges to measuring the mass of the Milky Way
One way to estimate the mass of the Milky Way, noted Dr. Eadie, is by studying kinematic tracers — in other words, studying the motion of tracer objects. A common kinematic tracer, she continued, is a globular cluster, or a cluster of stars.
A globular cluster moving through space has a velocity with two components — one from the observer’s line of sight and another in the plane of the sky, explained Dr. Eadie. However, astronomers do not always have measurements of both components, posing a challenge for calculations.
In addition, astronomers who measure this velocity do so from the reference frame of Earth. This is another problem, as they must translate these measurements to the reference frame in the centre of the Milky Way, in order to estimate the galaxy’s mass. A third issue is accounting for measurement error from instrumentation for scientists to avoid overconfidence with their results.
Astronomers also have different assumptions about the trajectories of globular clusters — whether they are more elliptical or circular —as they can take millions of years to complete an orbit, noted Dr. Eadie.
Finally, separate research teams also reported differing interpretations about the Milky Way’s mass, as they report these estimates using differing ranges from the galaxy’s centre.
A potential solution by Dr. Eadie’s research team
To tackle these problems of uncertainty, Dr. Eadie and her research team have developed a hierarchical Bayesian method — in other words, a way to apply probability theory to estimate the Milky Way’s mass.
“It allows us to include the measurement uncertainty and allows us to incorporate this incomplete data [of velocity components],” said Dr. Eadie.
Using data collected by the Gaia satellite, an observatory of the European Space Agency that has measured “the position and velocities of over two billion stars in the Milky Way,” Dr. Eadie and her collaborators successfully applied their model to provide an accurate estimate of the galaxy’s mass.
They reported their results in a research paper published in The Astrophysical Journal in 2018. “Doing this kind of analysis could help improve our interpretation [of the galaxy’s dark matter halo],” reflected Dr. Eadie, and help astronomers better evaluate the results of previous research papers about the Milky Way.
Studying dwarf galaxies to create a new estimate
Another focus of Dr. Eadie’s research team are the approximately 30 dwarf galaxies orbiting the Milky Way. Since they orbit the galaxy just like globular clusters, she noted that they “can also be used to measure the mass of the Milky Way.”
“If we can get their positions and velocities and then use a model for the gravitational potential, then we can infer how much mass is there,” she noted.
To create a new estimate, Dr. Eadie is collaborating with undergraduate Xander Dufresne and recent graduate Keslen Murdock at the University of Toronto; recent graduate Anika Slizewski and Dr. Mario Juric at the University of Washington; Dr. Robin Sanderson at the University of Pennsylvania; and Dr. Andrew Wetzel at the University of California, Davis.
“With this new data, we’ve been able to get a new mass estimate for the Milky Way,” she said. “and we’re finding that with the dwarf galaxies, we actually get a much larger mass estimate than we were before.”
“We’re currently trying to figure out exactly why that is, and also why some of these dwarf galaxies seem to play a large role in determining what the [Milky Way’s] mass is.”
Locating ultra-diffuse galaxies with statistical methods
Another aspect of the universe under the focus of Dr. Eadie’s research team is the existence of ultra-diffuse galaxies, which are a relatively recent discovery by astronomers. Scientists are interested in studying them further, especially as they do not yet have a clear understanding of how their formation fits with the evolution of the universe, noted Dr. Eadie — along with why many appear to have large amounts of dark matter, while others appear to have little.
However, due to the ultra-diffuse galaxies’ low emittance of light, astronomers find it difficult to detect them with standard telescopes, she continued. While NASA’s Hubble Telescope can detect them more easily, Dr. Eadie noted that it is competitive to book time on the instrument. Astronomers must therefore narrow down where to point the telescope to find these galaxies for imaging.
To develop a solution to this challenge, Dr. Eadie is collaborating to apply spatial statistics to develop a model for discovering ultra-diffuse galaxies with incoming PhD student Dayi Lee at U of T’s DoSS; Dr. Roberto Abraham at the DADAA; and Dr. Patrick Brown at the DoSS and the Centre for Global Health Research at St. Michael’s Hospital.