Category Archives: Latest News


Sorry for the delay in posting, I was knocked out for a few days with something but catching up now. So EHT did end up triggering the final night on 11 April! Things went really well, and one of the things I really wanted to see happen, happened! My main role in all this was to help organize and coordinate the “multiwavelength” observations, meaning trying to get telescopes in space and on the ground looking in other wavelengths (primarily X-ray and infared (IR) which are the only other bands besides radio that are visible through all the muck between us and the center of the Galaxy). We had a big overlap earlier in the week with EHT, Xray and IR that I posted about, but we didn’t end up seeing any changes. But on the last night, 11 April, we also had two premier X-ray observatories, Chandra and NuSTAR (that cover low and high X-ray energies, respectively) watching and lo and behold, a flare was seen, when EHT was watching too! This is very hard to achieve, because Sgr A* (the black hole I keep talking about) does these little bursts of emission called flares about once a day on average, but there is no predictable schedule. Sometimes there is no flare, sometimes there are four small flares, sometimes there’s a little “hiccup” and then a big flare. We still don’t understand what makes these flares, but from the short timescale (hours or less) we can figure out that it must be happening within 10s of Schwarzschild radii (equivalent to the event horizon for a non-spinning black hole) from Sgr A* itself. I have been studying these flares for coming up on 20 years now, since their discovery with Chandra in the year 2000, and we still don’t really know what is causing them. We are pretty certain that it has something to do with magnetic fields transferring energy to particles, but whether it’s a hotspot orbiting in the disk of infalling matter, or something relating to the presence of jets of plasma being ejected, is still not clear. Knowing the origin will help us build a better model of the physics near black holes, and help us also interpret the EHT images. So in some sense you can think of the flare as a “flashlight” that momentarily lights up things that might be too dark for us to see, and now having EHT observing at the same time means we might be able to actually see which part of the system is responsible. So I’m pretty excited about this, and it was an incredible feat of scheduling on the part of the X-ray folk, who had to basically take their best guesses after consulting with us, about how to point the telescopes and when. It typically takes 24 hours to change the complicated schedule and pointing of these beasts in space, so we didn’t have the option to just swing the thing around with minutes notice. Some facilities can do that, but not these.

Anyway, to end this thread of posts, instead of another picture of a telescope, I want to post a super groovy picture made to help illustrate the effect a spinning black hole has on spacetime, and how that distorts how things around it will look. This is the puzzle we need to solve effectively, so having these models is elemental to the process, we call it “general relativistic ray-tracing” because one has to trace individual rays of light from their origins to us, through the warped space time. How that works is based on Einstein’s theory of General Relativity, thus the name.

The image credit and description is: Bronzwaer, Moscibrodzka, Davelaar and Falcke, Radboud University 2017. This is an illustration of the gravitational lens of a Kerr (spinning) black hole (a = 0.99); the celestial map at infinity is a checkerboard pattern. In this image we can see the asymmetry induced by the black hole spin (in the shape of the horizon and the asymmetric background distortion). We can also clearly see the Einstein ring, the ring-shaped structure around the horizon.

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Drumroll please….

Ok I was too tired last night (or rather, early this morning) to complete my report from Amsterdam/EHT “Pajama Central Command” outpost, sorry to leave the ~10 people reading this in suspense! It turned out to be quite a harrowing situation. Shep (the PI) referred to it as a more typical “angst-ridden” decision, because the earlier nights had been pretty clear what to do. By the time we reconvened at 1:00am EU time, the good news was that the weather at LMT had begun to stabilize, and SMT was still a bit marginal but good to go. But then there was an O-ring problem on one of the helium dewars at JCMT on the top of Mauna Kea, a very high, isolated mountain where there aren’t exactly spare helium dewars just lying around! So they were working on jury-rigging a solution, and then the worst of all possible things happened: the correlator on ALMA went down. For those of you unfamiliar with this acronym soup, these are all the names of the different facilities across the globe being linked together into the “Event Horizon Telescope” experiment, to make an effectively earth-sized array. ALMA is the key part of that, a newish, extremely sensitive array in its own right in Chile that sort of anchors the whole project in terms of sensitivity. Without its correlator, the communication between ALMA’s individual dishes would be down, and no ALMA means no trigger. We had 45 minutes until the deadline for the final go/nogo decision, and it all depended on someone at the ALMA site figuring out the problem. They managed to reset the correlator and got it working, and the GO came out of Central Command at 2:17am, just a scant four hours before the observations had to start, so it was a very tight call. But I’m extremely happy, this means we got two consecutive days on said favorite black hole Sgr A*, both with EHT and the Xray missions, plus I found out there was also some TeV gamma-ray coverage from H.E.S.S.. It was also just super cool to be a (minor) part of this process and I will now hold my breath for the 6 (?) months until we know our results. Not really. About the breath I mean, the 6 months is probably not a bad estimate.

To end, another beauty shot posted by David Sanchez at the LMT in Mexico:

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Amsterdam/EHT Pajama Central Command Outpost

It’s a tense night here at the Amsterdam/EHT “Pajama Central Command” outpost! All sites have remarkably good weather except SMT (marginal but not terrible) and LMT (worse than marginal but potentially variable). The team decided to do a provisional “GO”, but are reconvening at 1:00am Europe time to see what things look like then. Given the Chandra and NuSTAR coverage I am really hoping the LMT weather improves. It’s a bit like watching a toaster, I keep checking the site opacity monitor and it’s very variable, but higher than the sustained 0.5 we want…

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Amsterdam Central Command

I am really excited, I get to participate in the go/no go decision tonight with EHT Central Command!! We’re going to decide if tomorrow is the big day for Sgr A* (remember, my favorite black hole), when we might observe for something like 10 hours. What is extra cool is that we have some overlapping coverage with three X-ray satellites in orbit (Chandra, NuSTAR, Swift), as well as hopefully also the VLT, which is the premier European-run optical/IR facility at the moment, in Chile. It is very hard to get so many instruments to look at the same object at the same time, so if all goes well we’ll have some amazing data to model!

Beauty shot by Heino Falcke from Pico Veleta near Granada, the big IRAM 30m dish.

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As if it weren’t enough…

So the first EHT run last night has gone really well, though of course there were a few technical issues. I really enjoyed being on the Slack channel and following the communications in realtime from all the stations across the globe. Not to mention the snarky comments (people competing between SPT and LMT for being a “big ungainly sail” when it comes to wind disrupting pointing accuracy…who knew??). But if that weren’t enough, the black hole X-ray binary Cyg X-3 decided to have a massive flare!! So at the 11th hour, with the folk having been up all night, there was a flash decision to point 3 telescopes (JCMT-SMA-SMT) of the full configuration at the source. So much great science, so little time!! Unfortunately the process of correlating the data and getting results is going to be very involved, so we won’t know what we saw for several months after the runs. Talk about delayed gratification.

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It’s official!

I just got back from a month at UT Austin as a visiting Tinsley Scholar, which was great. Two years ago I went for three months as a Tinsley Professor, and got to bring part of my research group with me, but this time was a smaller scale visit. I started two projects that I had been discussing for awhile, but now these have (I hope) legs. One is together with Prof. John Kormendy, and is being led by my former postdoc Dr. Rich Plotkin, now a senior fellow at Curtin University in Perth, Australia, and also includes Dr. James Miller-Jones, from the same institute. This paper involves a relationship I helped discover called “the Fundamental Plane of Black Hole Accretion” (see, e.g., Merloni, Heinz & Di Matteo 2003; Falcke, Körding & Markoff 2004; Körding et al. 2006 and Plotkin et al. 2012, if you are interested in more details). Basically if you make a three dimensional space where each axis represents, respectively, radio luminosity, X-ray luminosity and black hole mass, almost all black holes we know of that have compact jets lie on a two-dimensional plane in that space. This relationship gives us clues about how black holes release energy into different forms, and the coupling between what goes in and what goes out, so is very important to understand how black holes potentially impact their surroundings. It also tells us that black holes operate in “modes” that care more about the rate at which they are fed material than what their mass is. In other words, a black hole of a few solar masses will regulate its power output similarly to a supermassive black hole, as long as they are at a similar relative power (we can scale the power in a way that is independent of mass).

However there is some scatter in this relationship that we would like to understand better and, if possible, decrease. Also, people are increasingly using this relationship to determine the mass of newly discovered black hole candidates given observations of their radio and X-ray luminosities, in particular for objects that could be the hard-to-find intermediate mass black holes. But, the way we found the original Fundamental Plane was not actually well-adapted for this purpose. What we would like to do is a new study of the relation, using updated masses from Prof. Kormendy and collaborators, and then perform the statistics of deriving the plane relation in a way that the community can also use to find unknown masses.

The other project is with Prof. Volker Bromm, who is an expert in simulating stellar populations and feedback in the early universe. We are starting to think about how to better include the effects of early black holes in these simulations, particularly in terms of the accretion modeling. Most simulations just assume a fixed efficiency of heat dumped into the grid by a given black hole, and we are curious if better implementations of the physics will actually change the net result in the simulations.

But I digress…the main point of this post was that while I was gone, I found out that I had been promoted officially to full professor as of 28 February! This is a really nice thing, first of all because it means I get to wear a funny hat and robe (“toga”) at my students’ graduations! But more seriously, it means that in the byzantine Dutch system I can now be credited as the sole supervisor of my Phd students, while until now I had to have someone else who was full professor sign off as a formality. And it means I become one of just five (or six??) female professors at my university’s science faculty, something like 4% I guess. This number is still really low, even compared to other science faculties in the Netherlands, but it is slowly changing.

So anyway, sometime in the fall is an official ceremony called an “oratie” where I will give a public-level talk and there will be some kind of party after, stay tuned!

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Elected member of Science Council of the Event Horizon Telescope

The new group has arrived as of this week (woohoo!) and I will be adding some information about that as soon as possible, but in the meantime I thought I would just mention some news, which is that as of last month I have been elected to be a member of the Science Council of the international Event Horizon Telescope project.

This project is an ingenious idea to use the entire Earth diameter as a huge baseline for a telescope, using a technique called Very Long Baseline Interferometry (VLBI). Why do this? Because the larger your telescope is, the better you see, and in particular, the finer details you see.

VLBI has been done for many years in the radio bands, but it is very challenging at higher frequency (shorter wavelengths) primarily because the atmosphere changes in ways that affect those bands more, so there is a sort of background that confuses your ability to make a good image when one telescope in your array sees through a different piece of the sky than another. That’s where the ingenious part comes in: using supercomputers to correlate the data as well as new techniques to correct for these effects, it is now possible to move to higher frequencies like the millimeter and submillimeter. These frequencies just happen to be where the regions just touching on the Event Horizon (thus the name) of two nearby supermassive black holes are brightest: the black hole in the center of our Galaxy, Sgr A*, and the whopping huge one in the center of a nearby galaxy, M87. With the full array, already in prototype stage, we will be able to make the first ever images of regions on event horizon scales, quite possibly even seeing the “shadow” of the black hole where the light is sucked in, leaving a dark spot. But we also expect to test our ideas about how accretion (a fancy word for stuff falling inwards due to the pull of gravity) lights up the regions around black holes, which are subject to extreme space-time curvature due to the strong gravity, as well as extreme physical conditions like very high density and magnetic field strength.

If you can’t tell, I’m pretty excited about this project, so it’s an honor to have been invited to sit on the committee that helps define the science requirements, and advises on things like science priorities and working groups, in order to maximize the science output.

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Please make sure all your daughters read this (or any sexist bastard you know while we’re at it):

Ok, I realize that my language here is a bit politically incorrect, but sometimes you just can’t say it any other way.

Prof. Fiona Harrison kicks ass! She’s professor and the current department chair at the Astronomy/Physics Dept at Caltech, one of the top universities in the world. But more importantly, she designed a friggin’ space X-ray observatory, that had one of the most complicated launch manoeuvres possible, and it has worked so spectacularly that even as a small “cheap” mission it’s revolutionised my field! Today she was awarded a big prize by the international Committee on Space Research (COSPAR). Here’s the motivation, but it just makes me proud of her, and a great milestone for women in science:

“Fiona Harrison is the leader of NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array) mission, launched in June 2012. As the first focusing telescope operating in the hard X-ray band, NUSTAR is a hundred times more sensitive than any previous spacecraft in the 15 – 79 KeV spectral band. This has opened a new window on the Universe.

Among the most impressive results of NUSTAR and of Professor Harrison’s group are: 1) The first map of the Cas A supernova remnant in the radioactive line of Ti-44. The Ti-44 line was also detected by NUSTAR from the remnant of supernova 1987A in the Large Magellanic Cloud. 2) Due to the unprecedented angular and timing resolution, the NUSTAR team discovered emission from a magnetar – a neutron star with a magnetic field exceeding 10^14 Gauss very near the center of the Milky Way. This is the first pulsar discovered in the vicinity of our central Black Hole. 3) The majority of scientists believed that ultra-luminous X-ray sources in other galaxies are the black holes having a mass exceeding 1000 solar masses. Such black holes are impossible to create as a result of stellar evolution. The group led by Fiona Harrison discovered that the well-known ULX in the star forming galaxy M82 is an X-ray pulsar of period 1.37 seconds, and is one of two stars in the binary with a period of three days. We know that pulsars are neutron stars having masses usually less than 2 solar masses. This source has, at a maximum, the X-ray luminosity exceeding a hundred times the Eddington critical luminosity, i.e. the radiation force on the surface of this accreting neutron star exceeds a hundred times the gravitational attraction to the neutron star, an observation that has yet to find adequate theoretical explanation.

These and many other discoveries make Fiona Harrison one of the most active leaders of modern high energy astrophysics.”

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Big subsidy for the group!!

I was thrilled to find out last week (around the time of the big Gravitational Wave detection!!) that I was awarded a Vici grant from the Dutch National Research Organization (NWO), basically 1.5 million Euros to hire 3 PhD students and 2 postdocs over the coming 5 years! The title of my proposal was ““From micro- to megascales: understanding how black holes shape the local universe”, and focuses on how black holes release energy from stuff they gravitationally capture, and dump it back into their surroundings. There’s a nice description on the press release from our science faculty here.

So anyway we had our annual PhD recruiting last week and I’m happy to say I had some great candidates to choose from, from all over the world, for the first two PhD student positions! We have just made the offers so hopefully an update soon of the first new members of the group to come in the Fall!

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Public talk on top of the Oude Kerk! (Postponed!)

NEW:  Due to rain we are postponing this event until next week, probably Thursday or Friday 20 or 21 August.   Stay tuned by checking the website if you were interested.  I heard it sold out so I’m pretty excited to have a good crowd, but maybe with the date change there will be some cancellations…

Thanks to the folk at Non-Fiction, who organise many cultural events around Amsterdam, I will be participating in an exciting late night talk on top of the Oude Kerk (the Old Church), one of the oldest structures in the heart of Amsterdam! Non-Fiction are curating a series of cultural events in August and September in the evenings, using a really amazing (I got to view the space last week) art installation “The Garden Which is Nearest to God” built by Japanese artist Taturo Atzu. The series is called “Come Closer”. As part of it, on 15 August I will give a brief talk under the stars (hopefully not under the rain, in which case we may cancel) and if we are lucky we will see a few stragglers from the Perseid meteors. It is a very otherworldly space, I encourage you to check it out, even if not for my gig. Here is the program. You will need to get a ticket via the Oude Kerk.

Come Closer poster

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