Mayank Chhaya Reporting
The urge to report stories has not dimmed despite the passage of three and a half decades in the profession. I do it to keep it sharp.
The stories here are reported for other media outlets and republished here. Since I control the design and display on this site, it offers some creative flexibility.
By Mayank Chhaya
Alex Drlica-Wagner’s playground is between 1 million and 100,000 light years from Earth. Scouring at such distances in the immediate neighborhood of the Milky Way, Dr. Drlica-Wagner looks for the elusive dark matter.
His job has been somewhat trendily described as a “dark matter hunter”, searching for something that is believed to constitute 27% of the universe. Contrast that with the barely 5% constituted by baryonic matter or normal matter, of the kind that everything we can see and experience is made of. Add to this the scientific consensus that 68% of the universe is dark energy and one begins to get a measure of how important this dark world is.
What is even more fundamental is that there is scientific consensus that it is this yet undetected dark world which has ensured that hundreds of billions of galaxies and many trillions of stars do not eventually tear apart. Dark matter is that mysterious celestial glue that seems to hold things together.
Although the existence of dark matter has been postulated variously for four centuries since the 1600s, the way the scientific community understands and studies it was first suggested by the Swiss astronomer Fritz Zwicky in 1933. While studying the Comma galaxy cluster in 1933 and concluded that the gravitational mass of the galaxies in that particular cluster was 400 times greater than what their luminosity suggested. From that calculation Zwicky inferred the cluster had matter that could not be seen—dark.
“The general status has evolved a lot since then. We have a much better understanding of what dark matter is not and what it could be,” Drlica-Wagner told me in an interview at Fermilab. He is holds a PhD in physics from Stanford in “Searching for Dwarf Spheroidal Galaxies and other Galactic Dark Matter Substructures with the Fermi Large Area Telescope.” Currently, he is the Schramm Experimental Fellow at the Fermilab Center for Particle Astrophysics. He is a member of both the Dark Energy Survey (DES) and the Fermi Large Area Telescope (LAT). His primary research focus is the search for dark matter through indirect detection and astrophysical probes. In short, he knows a thing or two or may be even three about dark matter.
Drlica-Wagner explains that mass of objects such as galaxies or cluster of galaxies can be measured by how much light they produce or measuring how fast they are moving. “Gravitational attraction pulls objects harder and the harder it pulls the faster things go. So you would hope that those two methods would lead to the same mass,” he says. Unfortunately, they do not. There is a giant discrepancy between the two calculations, the way Zwicky had found.
How giant is that discrepancy? “It is roughly a factor of six that they are off by. So there is about six times more dark matter than what we can account for in what we can see,” he says. In a sense, all galaxies, stars, planets and everything else in the light world is cosmically groping about in the universe. That is what Drlica-Wagner and many others are trying to study.
Early on in the history of dark matter, it was thought that a lot of the actual objects made of baryonic matter could explain the missing mass; objects such as space rocks, asteroids, rocky planets and gas which do not emit much might and hence are dark. (Gas is hot and X-ray emitting but it is not in the optical range.)
“Could there be normal matter that cannot be seen? Over time we have gradually through various techniques narrowed down that it can’t really be normal matter that makes up all the dark matter. As instruments get better we find that there is some components of matter that is made up of things that we are not used to experiencing and is outside what we call the Standard Model of particle physics that make up this extra mass,” he says.
Drlica-Wagner says what is animating the debate is a search for a new particle that could be constituting dark matter. He clarifies that it is an “open question” whether it is a particle or particles. “It could be a single one. It could be more complicated,” he says.
In recent weeks and months, there appears to be a visible surge in the science media’s interest in dark matter because it remains one of astronomy’s big unresolved questions. Descriptions such as “the dark sector” or “the ghost world” with some loaded philosophical hints have gained ground. Could the realization that between dark matter and dark energy we barely know 5% of the universe be a source of intellectual exasperation? Drlica-Wagner answers that in the quintessential manner of a physicist which is to say without giving it any emotional underpinnings.
“It is more a sense of excitement and opportunity. It is a huge opportunity we have to make very large steps towards increasing our understanding of the fundamental building blocks of the universe. I don’t sit troubled in my chair worrying (about the emotional aspect of it). It is very exciting to try and actively seek out what the dominant components of the universe are,” he says.
One particular question that has deeply interested me is what astrophysicist such as Drlica-Wagner might expect to be the most striking feature of dark matter when they do eventually find it. “That’s a great question. The dark matter problem is an astrophysical problem. We see the signatures of this missing mass when we look out at the universe. There is another problem in particle physics, which is why do the particles, have the masses that they do? Why is that scale so different from some of the fundamental scales at which we believe particle physics operates? This is another big question in particle physics now where one of the possible solutions is that you have an entire spectrum of new particles that have not been discovered yet. This is often called supersymmetry. One thing that is very exciting is that perhaps these two problems that at first seemed disconnected could both be solved by the same extra particle. So the dark matter particle could also be a supersymmetric particle,” he says.
In terms of Dr. Drlica-Wagner’s specific observational work, he spends time at the Cerro Tololo Inter-American Observatory (CTIO) in the Chilean Andes where he was this June. He uses the observatory to look at dwarf galaxies between 1 million and 100,000 light years away in his quest for dark matter to collect upto 300 images every night. Dwarf galaxies in the Milky Way’s neighborhood are dark matter-dominated . His particular interest is searching for evidence of dark matter in gamma rays, using the Fermi Large Area Telescope (LAT). A backgrounder on his official page explains, “Dwarf galaxies are rich in dark matter but lack astrophysical gamma-ray production, making them prime candidates for dark matter detection. Additionally, numerical simulations predict that many more dwarf galaxies are yet undiscovered. Dark matter decay or annihilation in these galaxies would cause them to shine as unassociated gamma-ray sources.”
In the context of the pervasiveness of dark matter, he puts it in a strikingly picturesque manner. “We do live within a bath of dark matter. Similarly, we do live within a bath of neutrinos. Neutrinos are much lighter particles but they are similarly hard to detect. It took a very long time for us to detect neutrinos and then measure the very rare interactions that do occur as they pass through us all the time. The idea of dark matter is very similar that. There are these particles that interact very, very rarely and pass through us all the time,” he says.
One recurring question that I ask all physicists has to do with balancing the profundities of their professional work with the relative trivialities of everyday life. I was interested to find out how Dr. Drlica-Wagner, as preoccupied as he is with a staggering question like dark matter and spends time observing structures so far away, squares those with his mundane concerns. Also, in doing so does he not get bored? He was amused by the question even as he instantly understood its drift.
If my intention were to find out whether he can take mundane life seriously after being embarked on a fundamental search, he said, “One can turn the question around and ask whether what I observe 1 million light years away has any bearing at all on our normal daily lives. That is an equally important question.”
Dark matter is one of the big questions in astrophysics because its existence or otherwise is fundamental to what the universe may or may not be. It has fascinated me personally for decades as a dabbler in physics and I have written about it occasionally. As a prelude to two upcoming posts about dark matter the following is what I wrote on September 13.
Searching for dark matter that may or may not exist feels like a staggering paradox. It is believed to constitute some 27% of our universe. Add to this the scientific consensus that 68% of the universe is dark energy and you are left with just 5% of what we can directly see and/or experience in the universe.
That 5% includes all stars, galaxies, asteroids, dust, you, I and Hillary Clinton. Also, Donald Trump, Vladimir Putin and Kim Jong-un as well Kim Kardashian. My point is everything we can directly prove the existence of is just a niggardly 5%. Hence the search for dark matter. That search or at any rate deep interest in that search took me to the iconic Fermilab yesterday to meet Dr. Alex Drlica-Wagner. He holds a PhD in physics from Stanford in “Searching for Dwarf Spheroidal Galaxies and other Galactic Dark Matter Substructures with the Fermi Large Area Telescope.” Currently, he is Schramm Experimental Fellow at the Fermilab Center for Particle Astrophysics. He is a member of both the Dark Energy Survey (DES) and the Fermi Large Area Telescope (LAT). His primary research focus is the search for dark matter through indirect detection and astrophysical probes. In short, he knows a thing or two or may be even three about dark matter.
Today, I publish the first of the two posts which is my video interview with Dr. Drlica-Wagner. Given the space limitation of my phone I couldn't do more than 10 minutes of video which is what I present today. Tomorrow, I will publish a slightly larger story incorporating much of what he says here as well as other salient points he made beyond this interview.
In recent years, the search for dark matter has become a key area of astrophysics because of the sheer suspected scale of its existence. Now there are those who speculate that there could well be a whole dark world which is a parallel to our light world. This is the stuff of science fiction which could well become science fact. As Dr. Drlica-Wagner points out, if baryonic matter or normal matter of the kind that makes everything that we can see, including us, is complicated, there is no reason to think that dark matter will be something normal. So until we find dark matter and even a dark world and dark life, enjoy light. A more extensive story tomorrow.
My rendering of Proxima b orbiting its star Proxima Centauri 4.3 lightyears from us.
Proxima b "an ideal target” for exploring life outside Earth
I did the following interview for The Wire, one of India’s most respected news sites.
By Mayank Chhaya
The recent discovery of an Earth-sized planet orbiting Proxima Centauri, the star closest to the Sun, within within the star’s habitable zone has caused a lot of excitement among the international astronomy community.
Guillem Anglada-Escudé, an astronomer at Queen Mary University of London and leader of the team that made the discovery, says Proxima b, as the planet is called, is “an ideal target” to look for life on.
Located within a system that is just 4.3 lightyears, or 40 trillion kilometres, from Earth – a distance regarded as next door in cosmic terms – Proxima b is now among the most coveted exoplanets to determine habitability.
Proxima b is 1.3 times the mass of Earth and orbits its red-dwarf star every 11.2 days. Although the spectrographic evidence of such a planet has been observed since 2000, it was only in January 2016 that Anglada-Escudé and his team decided to make a definite determination using the European Southern Observatory (ESO) facilities. Between January 19 and March 31, they studied it for 20 minutes each night. The finding of their work was reported in the journal Nature to international headlines.
Adding to the excitement over the discovery are the expectations of a breakthrough in laser-propelled interstellar probes that can travel at 20% the speed of light, covering the distance to Proxima b in 20 years.
The question of whether life can actually exist on Proxima b is very much in the realm of speculation. Its distance, although relatively close to its star compared to Earth’s from the Sun, is mitigated by the fact that it orbits a red-dwarf star that is smaller and dimmer than the Sun. Its distance may make it friendly to liquid water on its surface but given that it is tidally-locked with its star makes thing much more difficult.
Being tidally-locked means it is always the same side of the planet that faces its star – the way the same side of the Moon does Earth. This causes a dramatic difference in surface temperatures between either halves of the planet.
For Anglada-Escudé, there is rather personal joy to discovering the planet because of his lifelong passion for such exploration, and his particular interest in a science fiction novel named Proxima by Stephen Baxter. The book is centered on a planet orbiting Proxima Centauri.
He answered questions from The Wire by email. Excerpts:
Is it fair to say that when it comes to exploring life on exoplanets there could not be a better location than Proxima b in terms of its proximity to Earth and given likely advances in laser-powered interstellar probes?
Yes, It is an ideal target because of proximity to Earth and also Star-planet contrast. The only drawback is that the orbit is relatively close to the star. Some direct imaging instruments might be able to resolve it, but it is really at the limit of current plans. However, designs might be slightly tweaked given that the planet is now known to be there.
In the very recent past, there have been a few possible candidates for Earth-like exoplanets but Proxima b seems most promising. Can you describe the fundamental features that you looked for to establish its credentials?
I would not say is the best Earth-like planet found so far. I would say this is one of the possibly Earth-like planets where we have better chances of getting more information. All boils down to its observational advantages. From a philosophical point of view, it would be way better detecting an Earth-like planet around more massive Sun-like stars (like the two Alpha Centauri stars, A and B), but observationally speaking at least we have realistic chances of being able to deduce some basic information from its atmosphere using near future observatories.
Would you describe the detection of starlight shift that helped you determine the existence of this planet?
We used the Doppler method. It consists on measuring the radial velocity of the star caused by its motion around the center of mass of the system. That is, the planet and the star orbit the common center of mass. What we measure is the back and forth motion of the star that follow the orbit of the planet.
Would it be accurate to say – if and when Proxima b’s friendliness to water and life is confirmed – that the circumstances under which life can evolve around the universe are pretty diverse and eclectic?
Yes. If by any chance we detect evidence of life on Proxima, is would very likely mean that the universe is full of inhabited planets. The contrary (absence of life) would not be very informative though. At least, if we get information on the putative atmosphere we can calibrate our models to narrow down the best spots for life.
I ask because in terms of their sizes and other parameters our sun and the red-dwarf around which Proxima b are so different. Also, one is struck by the orbital differences of our 365 days compared to Proxima b’s 11.2 days. And yet, it could also harbor life simply because the habitable distances are different.
The number itself is not that important. The compact orbit has consequences in terms of the tidal/rotation state of the planet. For example, we strongly suspect that it is synchronously rotating with the orbit in the same way the Moon is locked to Earth (we always see the same side). In this sense, we would have a side of the planet in permanent light and the other side on permanent darkness. The star would always be hanging from the same point of the sky. This has consequences on the possible climates but it has been found that it is not a major concern in maintaining a wet atmosphere.
You have been quoted as saying that there is a reasonable expectation that this planet may be able to host life. Do we have the ability to detect signatures of life from this distance in a broad sense or do we have to be on or close to Proxima b to be able to ascertain?
With the nextgen instruments we might be able to figure out the presence of a few molecules on the atmosphere of these planets. That is the next step. However, the presence of water and O2 only would not be a definitive evidence for life. What you need are chemical species that would be destroyed in the presence of the other (For instance, O2 + methane would react relatively quickly unless one of them is replenished). Out of equilibrium chemistry would be a really strong evidence for life on a given planet. Of course, we would still want to see it, but one step at a time.
How do you get around the datedness of the data given the time it takes light to travel from there to here, 4.3 years.?
We always see a delayed picture of the system. There is no problem on this because the delay is always more or less the same.
How do you compare the tug of Proxima b on its star to Earth’s on our sun? I am particularly interested in the numbers of the movement both cause on their stars?
Earth moves the Sun at 10 cm/s with a cycle of one year. Proxima b moves the star 1.5 m/s (at least) over an orbital cycle of 11.2 days. The combination of this larger signal with the shorter orbital period makes Proxima b much easier to detect that exact Earth analogs around Sun-like stars.
You have a lifelong passion for exploration of precisely the kind of planets that Proxima b appears to be. Also, you were drawn to Stephen Baxter’s book ‘Proxima’ which strangely foreshadows some of the very things that you might be on to. Describe to me how fiction and fact can converge in the most unexpected ways.
We were already hunting for the ‘signal’ at the time I found and read Stephen Baxter’s world. I found it rather amusing that the basic properties of the planet he describes were pretty close to the ones we were chasing. He makes up a lot of things but he based his world (called Per Ardua) on plausible climate models on scientific literature, so the world he describes is a plausible scenario (best case possibly…).
Can you describe the actual process of observation that you were engaged in? I believe you and team observed it 20 minutes every night between January 19 and March 31 this year using the ESO’s planet-hunting instrument. Do you actually peer into the sky using it or study the spectrographic information produced by this planet-hunting instrument?
We used HARPS installed at the 3.6m ESO telescope at La Silla [in Chile]. The observations were taken by an astronomer on site each night (We didn’t travel to the observatory this time). The only thing we see there are the spectra measured by HARPS.
We followed the star simultaneously with two other observatories (ASH2-SpaceObs and LCOGT). In these cases we did take images of Proxima (many hundreds of them!), but we used those to basically monitor its brightness and activity to be sure the activity was not related to the signal we were trying to confirm.
Finally, what more evidence would you be looking for now and if found, is it your expectation that we may mount an exploration in a reasonable future?
The most obvious thing we are trying to do is to see if the planet transits in front of the star. There is a small (but non-negligible) chance that this happens but it we need to be lucky. If that is the case, we could start characterizing its atmosphere before the end of the year! In the likely event that there are no transits, we will have to wait for E-ELTs and space-based instruments.
(Courtesy of www.thewire.in)