We run seminars on Thursdays from 2 - 3pm in the seminar room (30BB03) roughly every other week during the academic year. If you have any queries regarding the seminars then email Stacy Kim.

Upcoming seminars

In light of the COVID-19 pandemic and following the latest advice from the government relating to large gatherings, we have taken the decision to postpone all events. This decision currently applies to all events scheduled to take place between now and 31 May. Beyond that date, we will continue to follow government advice.

Past seminars

Nuclear stellar clusters and supermassive black holes

Speaker: Melvyn Davies (Lund Observatory)
Date: 12 Mar 2020

Abstract: Supermassive black holes are found in most galactic nuclei. A large fraction of these nuclei also contain a nuclear stellar cluster surrounding the black hole. Here we consider the idea that the nuclear stellar cluster formed first and that the supermassive black hole grew later. In particular we consider the merger of  stellar clusters to form a nuclear stellar cluster, where some of these clusters contain a single intermediate-mass black hole (IMBH). In the cases where multiple clusters contain IMBHs, we discuss whether the black holes are likely to merge and whether such mergers are likely to result in the ejection of the merged black hole from the nuclear stellar cluster. In some cases, no supermassive black hole will form as any merger product is not retained. This is a natural pathway to explain those galactic nuclei that contain a nuclear stellar cluster but apparently lack a supermassive black hole; M33 being a nearby example. Alternatively, if an IMBH merger product is retained within the nuclear stellar cluster, it may subsequently grow, e.g. via the tidal disruption of stars, to form a supermassive black hole.

General relativistic effects around the Galactic Centre black hole

Speaker: Stefan Gillessen (MPIE)
Date: 30 Jan 2020

Abstract: The Galactic Center offers the unique possibility to quantitatively test general relativity in the so-far unexplored regime close to a massive black hole. Here we present the results from the last two years of GRAVITY observations, in particular (1) the detection of the gravitational redshift in the orbit of the star S2, and (2) the orbital motion of matter close to the last stable orbit during a flare. The GRAVITY instrument, which we have developed specifically for the observations of the Galactic Center black hole and its orbiting stars, is now routinely achieving ~3 milli-arcsec imaging interferometry and with a sensitivity several hundred times better than previous instruments. Its astrometric precision of few ten micro-arcseconds corresponds to only few Schwarzschild radii of Galactic Center massive black hole, which opens up the possibility to test the fundamentals of gravity, all the way from the underlying equivalence principles, to considerations on new physics and their characteristic scales and strengths. The Galactic Center is and will remain the Rosetta-stone for deciphering strong gravity around massive black holes.

The discovery of a nearby 1700 km/s hyper-velocity star ejected from the Galactic Centre

Speaker: Sergey Koposov (Carnegie Mellon)
Date: 24 Jan 2020

Abstract: In this talk I will present a recent discovery of a new hyper-velocity star in the S5 survey. While the S5 survey is devoted to the study of the Milky Way stellar streams, the efficiency of target selection enabled us to target a large numbers of other potentially interesting targets. The search among those revealed a star with the radial velocity of ~ 1000 km/s. After combining the radial velocity measurement with the Gaia proper motion and spectrophotometric distance we found out that the star is more than twice as fast as other known hyper-velocity stars and its orbit can be for the first time confidently traced back to the Galactic Centre. The star was found to be ejected from Sgr A* ~ 5 Myr ago and can be possibly connected to the disk of young stars around the Galactic center.

Revealing the complex evolution of dwarf galaxies through spatially resolved spectroscopy

Speaker: Samantha Penny (Southampton)
Date: 16 Jan 2020

Abstract: Dwarf galaxies are the dominant galaxy population by number in the nearby Universe. Despite their ubiquity, the processes that govern their star formation activity are not well understood. In particular, what causes star formation to cease/quench in these low-mass galaxies? Addressing this question requires spatial information for dwarf galaxies in a range of local environments. Using data from the SDSS-IV MaNGA IFU survey, we identify a sample of quenched dwarf galaxies fainter than Mr = -19, selected independently of morphology and environment.  I will show the majority of quenched dwarfs exhibit coherent rotation in their stellar kinematics, and several host disc or spiral features, inconsistent with a primordial origin. I will also show that a number of bright dwarf galaxies with signatures of gas accretion host active galactic nuclei, which are likely maintaining their quiescence. While they are the "simplest" galaxies in our current models of galaxy formation, quenched dwarf galaxies are a diverse population, with further surveys and modelling needed to understand their origin.

Speaker: Andres Piatti (Astronomical Observatory of Cordoba)
Date: 3 Oct 2019

Stellar tidal streams outside the local group

Speaker: David Martinez Delgado (University of Heidelberg)
Date: 10 Oct 2019
Find out more.

Spin alignment of stars in old open clusters

Speaker: Enrico Corsaro (University of Catania)
Date: 7 Nov 2019
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Runaways from young star-forming regions in simulations and observations

Speaker: Christina Schoettler (University of Sheffield)
Date: 21 Nov 2019
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A geometric probe of cosmology: Gravitational lensing time delays and quasar reverberation mapping

Speaker: Angela Ng (University of Sydney)
Date: 12 Dec 2019
Find out more.

Speaker: Else Starkenburg
Date: 26 Oct 2017

Speaker: Mike Shara
Date: 1 Nov 2017

Speaker: Glenn Van de Ven
Date: 3 Nov 2017

Speaker: Chris Evans
Date: 9 Nov 2017

Speaker: Victor Debattista
Date: 23 Nov 2017

Speaker: Sergio Martinez
Date: 14 Dec 2017

Date: 22 Sep 2016
Speaker: Douglas Heggie (Edinburgh)

Date: 6 Oct 2016
Speaker: Luis Aguilar (IAE-UNAM)
Date: 2 Nov 2016

Speaker: Lucio Mayer (University of Zurich)
Date: 3 Nov 2016

Speaker: Rodrigo Ibata (Strasbourg)
Date: 10 Nov 2016

Speaker: Taysun Kimm (Cambridge)
Date: 24 Nov 2016

Speaker: Jackie Hodge (Leiden)
Date: 16 Feb 2017

Speaker: Clare Dobbs (Exeter)
Date: 2 Mar 2017

Speaker: Alis Deason (Durham)
Date: 16 Mar 2017

Speaker: Lia Athanassoula (Marseille)
Date: 18 Apr 2017

Speaker: Glenn van de Ven (MPIA)
Date: 18 May 2017

Speaker: Hans-Walter Rix (MPIA)
Date: 1 Jun 2017

Speaker: Chris Evans (ROE)
Date: 15 Jun 2017

Speaker: Paul Clark (Cardiff)
Date: 22 Jun 2017

Speaker: Jean Brodie
Date: 24 Sep 2015

Speaker: Holger Baumgardt
Date: 15 Oct 2015

Speaker: Peter Jonker
Date: 22 Oct 2015

Speaker: Chris Conselice
Date: 29 Oct 2015

Speaker: Greg Ruchti
Date: 5 Nov 2015

Speaker: Richard Alexander
Date: 19 Nov 2015

Speaker: Pierre-Alain Duc
Date: 26 Nov 2015

Speaker: Filippo Fraternali
Date: 3 Dec 2015

Speaker: Benjamin Moster
Date: 21 Jan 2016

Speaker: Melissa Ness
Date: 4 Feb 2016

Speaker: Stephen Wilkins
Date: 25 Feb 2016

Speaker: Nadine Neumayer
Date: 10 Mar 2016

Speaker: Alberto Sesana
Date: 7 Apr 2016

Speaker: Mark Wilkinson
Date: 21 Apr 2016

Speaker: Rosemary Wyse
Date: 5 May 2016

Speaker: Eugene Vasiliev
Date: 19 May 2016

Speaker: Denis Erkal
Date: 21 Feb 2015

Speaker: Alan Heavens
Date: 6 Mar 2015

Speaker: Monica Valluri
Date: 13 Mar 2015

Speaker: Claudia Maraston
Date: 3 Apr 2015

Speaker: Andrea Maccio
Date: 8 May 2015

Speaker: Jorge Penarrubia
Date: 15 May 2015

Speaker: Michela Mapelli
Date: 22 May 2015

Speaker: Daisuke Kawata
Date: 29 May 2015

Speaker: Laura Greggio
Date: 12 Jun 2015

Speaker: David Bacon
Date: 19 Jun 2015