Archive for black holes

PhD Opportunity in Theoretical Astrophysics at Maynooth!

Posted in Maynooth, The Universe and Stuff with tags , , , on January 18, 2023 by telescoper

Posting this again because the deadline (31st January) is coming up fast….

The Department of Theoretical Physics at Maynooth University invites applications for a PhD in Theoretical Astrophysics starting in September 2023. The successful applicant will work in the group led by Dr. John Regan on a project examining the formation processes of massive black holes in the early Universe. Massive black holes populate the centres of all massive galaxies and are now also observed in both the centres and in off-centre locations in less massive dwarf galaxies.

For more details and instructions on how to apply, see here.

PhD Opportunity in Theoretical Astrophysics at Maynooth!

Posted in Maynooth, The Universe and Stuff with tags , , , on December 8, 2022 by telescoper

The Department of Theoretical Physics at Maynooth University invites applications for a PhD in Theoretical Astrophysics starting in September 2023. The successful applicant will work in the group led by Dr. John Regan on a project examining the formation processes of massive black holes in the early Universe. Massive black holes populate the centres of all massive galaxies and are now also observed in both the centres and in off-centre locations in less massive dwarf galaxies.

For more details and instructions on how to apply, see here.

Job Opportunity in Computational Astrophysics at Maynooth!

Posted in Maynooth, The Universe and Stuff with tags , , on December 2, 2022 by telescoper

Just a quick post to advertise the fact that the Department of Theoretical Physics at Maynooth University is inviting applications for a Postdoctoral Fellowship Position in Computational and Theoretical Astrophysics. The successful applicant will join the Research Group led by Dr John Regan and is expected to develop their own independent research program within the confines of a research project investigating the formation, growth, and demographics of Black Holes in the early Universe. The group, currently consisting of four PhD students and one additional postdoctoral researcher, is currently engaged in numerous research topics with the goal of understanding early black hole formation. In line with this we are currently implementing an ambitious research project using the EnzoE exascale class code to run large volume, high resolution simulations focused on the first billion years of black hole formation. The successful candidate will be expected to contribute significantly to this research effort but are free to pursue their own research lines under this remit.

For more information, including deadlines and the applications procedure, please see the AAS Jobs register advertisement here.

New Publication at the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , , , , , , , , , , , on December 24, 2020 by telescoper

Just time before Christmas to announce another paper in the Open Journal of Astrophysics. This one was actually published a few days ago but because of holiday delays it took some time to get the metadata and DOI registered so I held off announcing it until that was done.

The latest publication is by my colleague* John Regan (of the Department of Theoretical Physics at Maynooth), John Wise (Georgia Tech), Tyrone Woods (NRC Canada), Turlough Downes (DCU), Brian O’Shea (Michigan State) and Michael Norman (UCSD). It is entitled The Formation of Very Massive Stars in Early Galaxies and Implications for Intermediate Mass Black Holes and appears in the Astrophysics of Galaxies section of the arXiv.

Here is a screen grab of the overlay:

You can click on the image to make it larger should you wish to do so. You can find the arXiv version of the paper here.

I think that will be that for for 2020 at the Open Journal of Astrophysics. We have published 15 papers this year, up 25% on last year. Growth is obviously modest, but there’s obviously a lot of inertia in the academic community. After the end of this year we will have two full consecutive years of publishing.

I’d like to take this opportunity to thank all our authors, readers, referees, and editors for supporting the Open Journal of Astrophysics and wish you all the very best for 2021!

*Obviously, owing to the institutional conflict I recused myself from the editorial process on this paper.

New Publication at the Open Journal of Astrophysics!

Posted in Maynooth, Open Access, The Universe and Stuff with tags , , , , , , on August 24, 2020 by telescoper

So another new paper has been published in the Open Journal of Astrophysics! This one is in the folder marked Astrophysics of Galaxies and is entitled Massive Star Formation in Metal-Enriched Haloes at High Redshift. I should explain that “Metal” here is the astrophysicist’s definition which basically means anything heavier than hydrogen or helium: chemists may look away now.

The authors of this paper are John Regan (of the Department of Theoretical Physics at Maynooth University), Zoltán Haiman (Columbia), John Wise (Georgia Tech), Brian O’Shea (Michigan State) and Michael Norman (UCSD). And before anyone asks, no I don’t force members of staff in my Department to submit papers to the Open Journal of Astrophysics and yes I did stand aside from the Editorial process because of the institutional conflict.

Here is a screen grab of the overlay:

You can click on the image to make it larger should you wish to do so.

You can find the arXiv version of the paper here.

Another Cosmologist for Maynooth!

Posted in Maynooth, The Universe and Stuff with tags , , on January 13, 2020 by telescoper

A few people have contacted me to ask what happened with the research position in cosmology at Maynooth University advertised a few months ago. Well, I am now in a position to provide the answer.

I’m very happy to announce that as of January 2nd 2020, Dr John Regan has joined the staff of the Department of Theoretical Physics, bringing with him an SFI – Royal Society University Research Fellowship (URF) which will fund his research for five years.

Dr John Regan

John’s primary area of research is in trying to understand the formation of black holes in the early Universe and their subsequent growth and evolution. He is interested in trying to determine how the first massive black holes in the Universe formed and the conditions required to form them. The problem is well posed since at early times the Universe was a comparatively simple place compared to the Universe today. Recent observations have indicated that Supermassive Black Holes existed less than 1 billion years after the big bang (the Universe is approximately 14 billion years old). A current open problem in Cosmology is how did black holes form and grow quickly enough in order to become super-massive so early in the Universe?

In answering this question John uses high resolution numerical simulations to study the environments in which the first massive black hole seeds may have formed and then grown to become the super-massive ones we can still observe today.

I’m delighted that John has joined the Department and look forward to many years of fruitful collaborations and discussions. He will be joined by a PDRA and a research student in due course.

You can follow John on Twitter here:

What to do if you find yourself inside the horizon of a black hole

Posted in The Universe and Stuff with tags , , , on May 7, 2019 by telescoper

Consider how lucky you are that life has been good to you so far.

Alternatively, if life hasn’t been good to you so far – which, given your current circumstances seems more likely – consider how lucky you are that it won’t be bothering you much longer.

That was the advice given to Ford Prefect by The Hitchhikers Guide to the Galaxy when he looked up `What do if you find yourself in a crack in the ground underneath a giant boulder you can’t move with no hope of rescue’. It seems fairly general advice to me, though. If you want more specific advice on what to do if you find yourself inside the horizon of a black hole then you can find it in an interesting paper on the arXiv with the abstract:

In this methodological paper we consider two problems an astronaut faces with under the black hole horizon in the Schwarzschild metric. 1) How to maximize the survival proper time. 2) How to make a visible part of the outer Universe as large as possible before hitting the singularity. Our consideration essentially uses the concept of peculiar velocities based on the “river model”. Let an astronaut cross the horizon from the outside. We reproduce from the first principles the known result that point 1) requires that an astronaut turn off the engine near the horizon and follow the path with the momentum equal to zero. We also show that point 2) requires maximizing the peculiar velocity of the observer. Both goals 1) and 2) require, in general, different strategies inconsistent with each other that coincide at the horizon only. The concept of peculiar velocities introduced in a direct analogy with cosmology, and its application for the problems studied in the present paper can be used in advanced general relativity courses.

It is advertised as a `methodological paper’ and I don’t know if they are planning experimental studies of this problem. I imagine might be difficult to secure funding.

On the Fellowship of Roy Kerr

Posted in The Universe and Stuff with tags , , , , , , , on April 18, 2019 by telescoper

Among the new Fellows of the Royal Society announced this week, I was astonished to see the name of Roy Kerr, the man who gave his name to the Kerr Metric an exact solution of Einstein’s equations of general relativity which describes the geometry of space-time around a rotating black hole.

When I say “astonished” I don’t mean that Kerr does not deserve this recognition. Far from it. I’m astonished because it has taken so long:the Kerr solution was published way back in 1963.

Anyway, better late than never, and heartiest congratulations to him!

While I’m on about Roy Kerr I’ll also say that I now think there is a very strong case for him to be awarded a Nobel Prize. The reasons are twofold.

One is that all the black hole binary systems whose coalescences produced gravitational waves detected by LIGO have involved Kerr black holes. Without Kerr’s work it would not have been possible to construct the template waveforms needed to extract signals from the LIGO data.

Second, and even more topically, the black hole in M87 recently imaged (above) by the Event Horizon Telescope is also described by the Kerr geometry. Without Kerr’s work the modelling of light paths around this object would not have been possible either.

The Shadow of an Event Horizon

Posted in The Universe and Stuff with tags , , , , , on April 9, 2019 by telescoper

There is a paper on the arXiv written about 5 years ago called Towards the event horizon – the supermassive black hole in the Galactic Center by Falcke and Markoff, the abstract of which reads:

The center of our Galaxy hosts the best constrained supermassive black hole in the universe, Sagittarius A* (Sgr A*). Its mass and distance have been accurately determined from stellar orbits and proper motion studies, respectively, and its high-frequency radio, and highly variable near-infrared and X-ray emission originate from within a few Schwarzschild radii of the event horizon. The theory of general relativity (GR) predicts the appearance of a black hole shadow, which is a lensed image of the event horizon. This shadow can be resolved by very long baseline radio interferometry and test basic predictions of GR and alternatives thereof. In this paper we review our current understanding of the physical properties of Sgr A*, with a particular emphasis on the radio properties, the black hole shadow, and models for the emission and appearance of the source. We argue that the Galactic Center holds enormous potential for experimental tests of black hole accretion and theories of gravitation in their strong limits.

Please note that the black hole in the centre of the giant elliptical galaxy M87 is about 1000 times further away from us than the black hole in the centre of the Milky Way but is also about 1000 times more massive, so its Schwarzschild radius is 1000 times larger. The observational challenge of imaging the event horizon is therefore similar in the two cases.

You may find this useful if, by sheer coincidence, there is some big announcement tomorrow..

Simulation of the binary black-hole coalescence GW170104

Posted in The Universe and Stuff with tags , , , on June 2, 2017 by telescoper

Via the Cardiff University news website, I found this video of a computer simulation of the binary black-hole coalescence that gave rise to the gravitational wave event GW170104 whose detection was announced yesterday, so I thought I’d share it here.

Here’s the  blurb accompanying the video:

The video shows a numerical simulation of a binary black-hole coalescence with masses and spins consistent with the GW170104 observation. The strength of the gravitational wave is indicated by elevation as well as color, with blue indicating weak fields and yellow indicating strong fields. We rescale the amplitude of the gravitational wave during the simulation to show the signal during the entire animation not only close to merger, where it is strongest. The sizes of the black holes are increased by a factor of two to improve visibility. The bottom panel in the video shows the gravitational waveform starting at frequency of 25Hz. The fade in of the video corresponds to a frequency of about 30Hz.

© Numerical-relativistic simulation: S. Ossokine, A. Buonanno (Max Planck Institute for Gravitational Physics) and the Simulating eXtreme Spacetimes project; scientific visualization: T. Dietrich (Max Planck Institute for Gravitational Physics), R. Haas (NCSA).

The colour scheme gives me a headache, and there’s no sountrack, but it’s quite instructive nonetheless.