In this thesis, we use low-frequency and high-frequency radio observations to address the following questions regarding quasars: is the radio loud/quiet quasar dichotomy real?

This thesis is a (biased) journey through very different topics in astrophysics: quasars and new populations of active galactic nuclei, gravitational waves from merging black holes, and protoplanetary discs around young stars.

An international team of astronomers, including Leiden PhD student Elia Pizzati, has observed several ancient quasars that, surprisingly, appear to be floating alone in the early universe (less than a billion years after the Big Bang). Until now, astronomers, based on models, assumed that quasars are…

Astronomers from Leiden Observatory have developed a new method to find distant quasars and better distinguish them from other objects that look like them, using machine learning techniques. The research result has been accepted for publication in the journal Astronomy & Astrophysics. It is the last…

Promotor: J.S. Kaastra Co-promotor: E. Constantini

In this thesis new methodologies are developed for the detection and systematic study of radio sources in the early universe. This allows us to gain a deeper understanding of the formation and evolution of galaxies, the activity of supermassive black holes, and the final phase transition of our universe:…

This thesis investigates the interplay between high-redshift quasars and the intergalactic medium (IGM) during the Epoch of Reionization (EoR). It combines new observations, systematic measurements, and forward modeling to constrain the physical state of hydrogen in the early Universe.

Tracing the evolution of the molecular gas content in galaxies is critical for a complete understanding of galaxy formation and evolution, as it provides the direct fuel for star formation. Studies of high-redshift (z>1) molecular gas reservoirs, most commonly traced by carbon monoxide (CO), have seen…

Promotores: Prof.dr. J. Schaye & Prof.dr. C. Steidel (California Institute of Technology)

Outflows are crucially important for the gas budget and evolution of luminous star-forming galaxies and AGNs, with observed mass outflow rates of the same order as the star formation rate. Greater star formation and black hole growth lead to more intense feedback and outflows, resulting in self-regulated…

I have studied the hot, diffuse gas around and between galaxies. Specifically, I have used the EAGLE numerical simulations of galaxy formation to predict the properties of this gas, and I have used those properties to predict specific observables: soft X-ray absorption and emission lines.

Galaxies form and evolve through close interaction with their surroundings. As a result, the heavy elements ('metals') that are synthesized in stars, are found both inside and outside galaxies.

Meet the newest Full Professor at the Leiden Observatory: Joe Hennawi. All the way from Santa Barbara, California, Hennawi will strengthen the astronomy institute. In Leiden, he will use his recent ERC Advanced Grant to study how supermassive black holes come into existence.

An international team of astronomers led by Matus Rybak (Leiden University) has proven, thanks to accidental double zoom, that millimetre radiation is generated close to the core of a supermassive black hole. Their findings have been accepted for publication in the journal Astronomy & Astrophysics.

PhD defence

Astronomers from, among others, SRON and Leiden Observatory have discovered long-sought intergalactic gas with ESA’s space telescope XMM-Newton. This gas is one of the pieces of the puzzle to map the total amount of ‘normal’ matter in the universe. The research will be published in Nature on 21 June…

It is an established fact that the Standard Model has to be extended to explain the so-called Beyond the Standard Model (BSM) phenomena: dark matter, matter-antimatter asymmetry of the Universe and neutrino flavour oscillations.

It's one of the big cosmology debates: the universe is expanding, but how fast exactly? Two available measurements yield different results. Leiden physicist David Harvey adapted an independent third measurement method, using the light warping properties of galaxies predicted by Einstein. He published…

How do stars and galaxies form? What is dark matter? To answer these and other questions, we need increasingly large telescopes. And to build these, we need international partnerships. A series on the impact of collaboration.

An international team of astronomers from Leiden Observatory and others, has for the first time mapped a piece of the dark, cosmic web. The research strengthens the hypothesis that the young universe consisted of huge numbers of small groups of newly formed stars. The astronomers publish their findings…

The European Space Agency (ESA) has published an interim data release from Gaia, the space telescope mapping out the Milky Way in 3D. The first scientific papers published today reveal half a million stars in the Omega Centauri globular cluster, nearly 400 candidate gravitational lensers and the positions…

Today, ESA’s Gaia mission releases its new treasure trove of data about our home galaxy. Astronomers, led by the Leiden astronomer Anthony Brown, describe strange ‘starquakes’, stellar DNA, asymmetric motions and other fascinating insights in this most detailed Milky Way survey to date.

After 25 years, December will finally see the launch of the long-awaited James Webb space telescope. Leiden astronomers are watching with great excitement: not only were they involved in the construction of important instruments on board, the telescope will also reveal many new secrets of the universe,…

It is still not easy to ‘come out’ about your sexual orientation or gender identity. On Coming Out Day (11 October), the issue was the focus of global attention. This year, instead of the traditional rainbow flag, the ‘progress pride flag’ flew above University buildings.

ESA’s space telescope Gaia, which maps the Milky Way, completes its active phase of scanning the sky on 15 January. Over the past decade, Gaia has made more than three trillion observations of about two billion stars and other cosmic objects. ‘Gaia is already the discovery machine of the decade,’ Leiden…

Leiden astronomer Anthony Brown had the honour to give the prestigious Spitzer Lectures at Princeton University. In five lectures spread over the beginning of May, he gave an insight into the Gaia Mission. ‘One of the intellectual highlights of the year.’

He makes music, goes to the athletics track twice a week and, according to his supervisor, has done his research so well that it would not be out of place in a PhD research. Physics and astronomy student Hidde Stoffels' undergraduate research on the properties of dark matter is of such high quality…

How can you see something that’s invisible? Well, with Euclid! This future ESA telescope will map the structure of the Universe and teach us more about invisible dark matter and dark energy. Scientific coordinator of Euclid and Leiden astronomer Henk Hoekstra explains how this works.

Professor Lodewijk Woltjer passed away on 25 August 2019.

We are grief-stricken that our PhD student Maolin Zhang passed away during the early morning of January 17th 2019. He died during a terrible fire that took place at his house in Hillegom.

Lecture, Oort lecture