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HU Astrophysicists Investigate the Expansion of the Universe

A telescope with a special-purpose camera scans for exploding stars

This ‘first light’ image was taken on
1 November 2017 using the new camera
after it had been installed in the 1.2-metre
Samuel Oschin Telescope at Palomar
Observatory in California. Each ZTF image
covers a section of the sky that could
encompass 247 full moons. The Horsehead
Nebula in the Orion constellation is easily
recognisable. The head of the horse faces
another well-known nebula, the Flame
Nebula. Source: Caltech Optical

Every night, a telescope with an extremely high-resolution camera will now search the cosmos for supernovae, accreting black holes and other short-lived, energetic celestial events. The camera – named the ‘Zwicky Transient Facility’ (ZTF) – is able to observe hundreds of thousands of stars and galaxies simultaneously and thus survey the night sky particularly quickly. The ‘first light’ from 1 November 2017 – i.e. the first camera short – shows a section from the Orion constellation, including the famous Horsehead Nebula.

Several international partners are involved in surveying the night sky: the Humboldt Universität zu Berlin (HU) and the German Electron Synchrotron (DESY) in Germany as well as the California Institute of Technology (Caltech) in the USA. This is also where the telescope is located.

“A lot is happening in the night sky,” says ZTF Chief Scientist Shrinivas Kulkarni, Professor for Astronomy at Caltech. “A supernova actually explodes somewhere in the universe every second. Naturally, we can’t see them all – but with the ZTF camera, we expect to be able to observe tens of thousands of them during the three years of the project.”

Short-lived celestial events, such as stars that explode in a supernova, are of particular interest,   not least because they act as cosmic particle accelerators and also enable us to measure the history of expansion of the universe. These are both areas in which the astroparticle physicists are also researching at the HU.

“Capturing the light from cosmic fireworks allows us to enter a new era of multi-messenger astronomy – investigating astronomic objects with light, gravity waves and neutrinos,” explains Marek Kowalski – Professor for Experimental Astroparticle Physics and Cosmology at the HU and Lead Scientist at the DESY. “I am very much looking forward to the first ZTF observations of the quickly fading blue flashes caused by merging neutron stars or the longer flaring from the supernova explosions of high-mass stars.”

His colleague Jakob Nordin, likewise Astroparticle Physicist at the HU who is responsible for calibrating the ZTF camera, adds: “Our Milky Way races through the cosmos at around 600 kilometres per second, and we ultimately don’t know why we are moving at such high speeds. We want to use the supernovae observed by the ZTF camera to improve our understanding of the influence the universe has on how our galaxy moves.”

Project participants

Half of the financing for the Zwicky Transient Facility survey project is provided by the National Science Foundation of the USA. The other half comes from various partners: including the Weizmann Institute in Israel, the Oskar Klein Centre at the University of Stockholm, the University of Maryland, the University of Washington, the DESY and the Humboldt Universität, the Los Alamos National Laboratory, the TANGO Consortium from Taiwan, the University of Wisconsin and the Lawrence Berkeley National Laboratory.

The Zwicky Transient Facility (ZTF) telescope camera

The survey project is named after the astrophysicist Fritz Zwicky, who came to the California Institute of Technology in 1925 and discovered a total of 120 supernovae over the course of his life. The Schmidt-type telescope spans 1.2 metres in diameter and is situated at the Palomar Observatory of Caltech. The new ZTF camera has a particularly large field of vision of 47 square degrees, which is 247 times larger than the full moon appears in the sky.

Thanks to this large field of view, the extremely sensitive camera and a quick telescope motor, the telescope will be able to scan almost the entire night sky for short-lived, dynamic events every three nights. Each image taken by the camera measures 24,000 by 24,000 pixels. To display an image in full resolution, 72 ultra-high-definition monitors would have to be connected together. The design and construction of such an installation posed a technical challenge, particularly due to the fact that the camera had to fit in the relatively narrow telescope tube. A range of new solutions had to be found. For instance, the camera shutter – normally installed directly in front of the camera – is placed outside the telescope and therefore had to be built incredibly large. With an aperture of 1.2 metres in diameter, it was necessary to build the largest camera shutter ever for astronomic purposes.

Further information

Website The Zwicky Transient Facility

Website EAT – The Cosmology group of the Humboldt Universität


Prof Dr Marek Kowalski
Institute for Physics

Tel.: 030 2093-7635

Press contact

Press Office
Humboldt University of Berlin

Tel.: 030 2093-2345