Teenage Galaxies

Hello, I am Dr Myrto Symeonidis a postdoctoral researcher at UCL’s Mullard Space Science Laboratory (MSSL), and this week I will be telling you about some of my research here at MSSL on galaxies “in their teenage years”: some of the youngest, dustiest and most energetic, galaxies in the Universe.

Infrared Radiation

For most people, the word “astronomy” brings to mind beautiful, colourful images of galaxies taken by the Hubble Space Telescope. Those images are usually showing you what galaxies look like in the optical part of the  electromagnetic spectrum. However, few people realise that what we can “see” with our own eyes is only a very small part of the picture.

EM Spectrum from http://en.wikipedia.org/wiki/Electromagnetic_spectrum

In fact, more than half of the total light produced by all galaxies in the Universe since the beginning of time emerges as infrared radiation, invisible to the human eye. The reason is dust.

Cosmic dust is somewhat of a misnomer; unlike the dust that you find in your home which has many constituents, cosmic dust is a conglomeration of tiny grains of rock-like material typically of carbon and silicon. It is prevalent in all galaxies and readily absorbs ultraviolet and visible light, subsequently re-radiating it in the infrared. Discovering the dust-obscured side of the Universe was one of the major scientific breakthroughs of the last century, enabling us to make immense progress in our understanding of the cosmos.

Star Formation or Supermassive Black holes?

Since the start of my career in astronomy I have been very keen to make sense of the role of dust in galaxy formation and evolution. One reason is that the dust content of a galaxy is intricately linked to its ability to make new stars, what astronomers refer to as the ‘star-formation rate’. The most dusty galaxies appear to make the most stars, which means that, on a cosmic scale, dust-rich galaxies are the main contributors to the total  cosmic energy budget. The other main way in which galaxies release energy into the cosmos are through Active Galactic Nuclei (AGN). This is a mundane name for an awesome phenomenon: AGN are supermassive black holes (many billions of times the mass of the Sun) that reside in the centres of galaxies and devour all infalling matter. In the process of consuming matter, AGN release copious amounts of energy. To understand the energy content of the Universe we therefore need to disentangle the contributions from star formation and AGN.

Measuring star-formation rates in galaxies that host AGN is a challenging feat because in many cases the AGN is luminous enough to completely drown the stellar emission from its host. To make things even more challenging, dusty galaxies were far more common in the early Universe, and thus identifying and studying them requires cutting-edge observational facilities to look back in time.

Herschel and the Rosetta Nebula from http://spaceinimages.esa.int/Images/2010/04/Herschel_and_Rosette_Nebula

The Herschel Space Observatory 

We are now fortunate to be living in the most data-rich era that infrared astronomy has ever seen, thanks to the Herschel Space Observatory, one of ESA’s most ambitious missions. Herschel is the largest space telescopes ever launched and is the only facility to date and for the foreseeable future that can span the part of the electromagnetic spectrum in which most of the Universe’s radiation from galaxies emerges.

MSSL has had a major role in the Herschel mission since its conception, with particular involvement in designing and building Herschel’s Spectral and Photometric Imaging receiver (SPIRE). Seeing the planing, building and eventual scientific results from space missions is one of things that makes MSSL such an exciting place to work.

The mechanical and thermal engineering group at MSSL assembled and tested the whole SPIRE structure, additionally providing key components such as thermal straps, detector boxes, mirror mounts and filter holders. Moreover, since Herschel’s successful launch in 2009, the MSSL astronomy group has been heavily involved in the exploitation of Herschel data with a strong focus on measuring the physical attributes of the primary energy production mechanisms in dust-rich galaxies, determining how these mechanisms interact and charting the changes in their characteristics back to when the Universe was less than a quarter of its current age.

With the advent of Herschel, we have been able to exploit the far-infrared part of the electromagnetic spectrum, where the energetic balance between AGN and star-formation tilts towards the latter. Taking advantage of Herschel data in a recent project that was led by the MSSL Herschel team, we were able to measure the star-formation rates of the galaxies which host the most powerful AGN at the time when the Universe was less than half its current age.

We discovered that although the host galaxies of AGN experience intense star-formation, if the AGN becomes powerful enough it seems that it is able to slow down and eventually terminate the star-formation, placing the whole galaxy in a rapid course towards old age.

An artistic impression of an AGN from here http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=5033

Although we still have a long way to go with respect to solving the mysteries of the cosmos, thanks to Herschel we are now step closer to understanding how galaxies evolve, from young ,dusty and active into old age.





Standby for the Universe’s Most Powerful Explosions

Welcome to our first science blog post. I am Dr Samantha Oates, a postdoctoral researcher at MSSL, investigating what we can learn about Gamma-ray Bursts (GRBs) from their X-ray and optical/UV afterglow emission. As our first science post, I shall introduce you to these enigmatic events, why and how we study them, and what we do at MSSL as part of the NASA Swift team.

What are Gamma-ray Bursts?

GRBs are the most extreme explosions in the known Universe. These events release as much as 1055 erg within a few seconds in the form of gamma-rays. This is significantly more energy than the Sun contains and releases over its entire lifetime (~11 billion years). The duration of this prompt gamma-ray emission roughly divides GRBs into long (>2 seconds) and short (<2 seconds) classes. The long GRBs are associated with the deaths of massive stars, while the short GRBs are associated with the merger of two compact objects, such as Neutron Stars or a Neutron star and a Black Hole (see Fig 1). GRBs appear to occur randomly throughout time and space. The furthest detected so far is at redshift 9.4, approximately 13.14 billion years ago (Cucchiara, et al., 2011, ApJ, 736, 7), when the Universe was about 5% of its present age.

The different sources and processes resulting in long and short GRBs. Credit: NASA and A. Feild
The different sources and processes resulting in long and short GRBs. Credit: NASA and A. Feild

Why Study GRBs?

During a GRB, relativistic jets, moving at 99.999% of the speed of light, are produced and a black hole is formed. Both these features are extreme situations that cannot be reproduced on Earth. GRBs thus enable us to examine processes that cannot be studied under laboratory conditions and enable us to test our understanding of physics. GRBs can also help us to understand the formation and structure of matter in the Universe. Because long GRBs signify the deaths of massive short-lived stars, they are thought to trace where stars form in the Universe. And as they can be observed over almost all cosmic time, they can be used to probe star formation, from the present through to the earliest times, even, in principle, before the first galaxies formed. Being able to detect them over cosmic history means we can also use them as standard candles to probe the expansion history of the Universe. In particular, long GRBs can be used to extend the Hubble diagram (distance versus redshift) beyond the limit of Type Ia supernovae (the Noble prize in Physics was awarded in 2011 for research using the Hubble Diagram and Type Ia supernovae). Another exciting prospect is that short GRBs could be the first sources for which gravitational waves are detected and confirmed.

What do we use to observe GRBs?

The unpredictability and the rapid fading nature of GRBs means that specialized instruments are necessary to detect and observe these spectacular events. Here at MSSL, we are involved in NASA’s Swift satellite, a GRB dedicated mission, designed to catch GRBs on the fly. Swift’s wide field detector (the Burst Alert Telescope; BAT) views ~1/6th of the sky for the prompt gamma-ray signal. Upon detection, Swift stops looking at its present target, and within a few tens of seconds has slewed to point its two narrow field instruments at the location of the GRB. These instruments, the X-ray Telescope (XRT) and the Ultra-violet Optical Telescope (UVOT), then observe the accompanying afterglow at X-ray and optical/UV wavelengths. The X-ray and optical/UV emission may be observed typically for a few hours to days after the prompt gamma-rays, and, in a small number of cases, up to several weeks. Swift detects on average 2 bursts per week. The rest of the time Swift performs a set of pre-planned observations, or follows targets of opportunity requested by the astronomical community.

What is MSSL’s involvement in Swift?

The UK has had direct involvement with the design and construction of the both the XRT, at the University of Leicester, and the UVOT here at MSSL. MSSL therefore has a responsibility to help calibrate the UVOT and to provide mission support. Part of that support involves analyzing the UVOT data following a GRB and also becoming “Burst Advocates“. A Burst Advocate is required to report on observations of a GRB made by Swift and other telescopes at the Swift daily planning meeting so that the operations team know whether to continue observing. At MSSL, our responsibility is to analyze UVOT data for GRBs occurring every other week and for one week in ten to be on-call as Burst Advocates.


NASA Swift mission logo. Credit: NASA
NASA Swift mission logo. Credit: NASA

How do we Chase GRBs?

Since GRBs can occur at anytime day or night and fade very rapidly, there must always be always be someone on-call so that the community can be informed, within minutes, on the location and brightness of the GRB in the gamma-ray, X-ray and optical/UV bands. It is the Burst Advocates responsibility to make sure that all the necessary information is promptly released, enabling the astronomical community to follow the event with other ground-based telescopes. For one week in every ten MSSL are Burst Advocates, this means someone has to be available to respond to Swift alerts, sent by email and text message, at any time, day or night, during these 7 days. While each GRB is very exciting and has the potential to help us understand different aspects of how these events work, I do wish they would wake me up less often at 5 am when I am on duty :-D

Swift has detected over 700 GRBs, since launch in November 2004, and has so far been a very successful and productive mission both for the GRB community and the astronomical community in general. At MSSL, we hope there are many more productive years for Swift to come.

Go for Launch!


Welcome to the MSSL Astrophysics Blog!

In this blog we will talk about all the amazing astronomy research that happens at MSSL. MSSL is UCL’s department of Space and Climate Physics, located in the Surrey Hills in the UK. MSSL is an interesting place to work, and we work on a vast range of astronomy projects. The department also builds components for satellite missions. In fact MSSL is one of the oldest and most well established space science departments in the world, and the largest in the UK.

We will also talk about our lives as PhD students, postdoctoral researchers and academic staff. What is it like to work at the cutting edge of research? What is it like to live and work in an area of outstanding natural beauty? How and why are we researching astronomy, and what motivates us? What were our career paths like, and what advice can we give? These are all questions that we will answer in the fullness of time.

Every two weeks you will find a new blog post. If something particularly interesting happens here, for example we always have interesting seminar speakers, a new satellite mission gets launched, or if people make profound discoveries in astronomical research – we will be sure to let you know!