At the Hamburg Observatory, the SHIPS experiment initiates a new era of astronomical observations – the search for hidden photons. These are a category of so far hardly explored elementary particles of possibly fundamental physical and astrophysical significance. The SHIPS experiment goes on the hunt for these mysterious particles which might be responsible for so far incomprehensible phenomena in the universe, and perhaps are a component of the ominous dark matter. For this purpose, a telescope will be used in which light must not penetrate.

Neu trifft auf alt: Das SHIPS-Teleskop ist auf das Oskar-Lühning-Teleskop der Hamburger Sternwarte montiert.

“With SHIPS, we create a completely new category of astronomical observatory stations for these hypothetical but extremely fascinating elementary particles,” states Günter Wiedemann from the University of Hamburg Observatory, responsible for the experiment. “The project is a successful synthesis of theory, experiments and astrophysics. We are now able to operate the telescope after a relatively short building time, and this is also due to the considerable engagement of our students and doctoral students.” SHIPS stands for Solar Hidden Photon Search. Apart from the Hamburg Observatory, scientists from DESY and the Max Planck Institute of Physics (Munich) are participating in SHIPS.

Hidden photons are elementary particles which only interact weakly with normal matter; their existence and behavior is being postulated and described by theoretical models. “According to theory, a whole series of hidden light particles may exist, but could so far not be verified experimentally,” said Andreas Ringwald (DESY), head of the project, jointly with Günter Wiedemann. “These particles could represent dark matter, as stipulated by numerous observations, making up about one fifth of our universe.”

The hidden photons emerge in large quantities in bright objects like the sun. They are able to change their state – similar to neutrinos, which are better known for this effect – and with a very low probability, transform into normal (electromagnetic) photons. These can be detected with a quasi-astronomical telescope. For this search, the Hamburg Observatory recently installed and put into test operation the first “Telescope for Solar Hidden Photon Search“ TSHIPS I.

The sought-after particles are observed in a long evacuated optical reaction chamber focussed to the sun. Because of the presumably very weak signals and as only the photons originating in the telescope are to be detected, the optics and the extremely sensitive detector must be thoroughly shielded against any surrounding light. Interestingly enough, TSHIPS I is a light particle telescope into which light from outside must not enter.

Now, one year after the project launch, a series of performance tests are carried out, followed by scientific observations. The scientists expect first significant measurements after a few weeks.

With the “Solar Hidden Photon Search“ project SHIPS, scientists from the Hamburg Observatory and DESY intensify their collaboration which started with the “Any Light Particle Search“ (ALPS) project. SHIPS is a sub-project of the special research project 676 “Particles, Strings and the Early Universe” of the University of Hamburg, funded by the Cluster “Connecting Particles with the Cosmos“ of the State Excellence Initiative LEXI.

Hidden photons

Hidden photons belong to a category of very light (and even massless) particles, predicted by the string-theory-inspired extensions of the Standard Model of particle physics. According to this theory, photons will sporadically change their state and oscillate between the common electromagnetic state and the very rare “hidden” state.

Accordingly, in bright objects like the sun, large quantities of hidden photons emerge from normal electromagnetic photons which, while migrating undisturbed, with a low probability change into normal light particles. The regenerated particles of initially solar origin are now to be detected with SHIPS.

TSHIPS: a telescope for SHIPS

At the first stage of the SHIPS experiment, a 2-metres-long steel pipe with a specially designed, weight reduced pipe of hexagonal structure was combined to a 4-metres-long vacuum helioscope, and connected to the fully movable and remote controlled mounting of the Oskar Lühning Telescope of the Hamburg Observatory.

In the first version the required optics are realised with large Fresnel lenses; low-noise photomultipliers and novel electron multiplication CCD’s are used as detectors.

The symmetric design with double optics and detectors allows using the telescope simultaneously in opposite directions. The sought-after particles penetrate the Earth almost undisturbed, which makes it theoretically possible to observe the sun continuously, also at night, even though the Oscar Lühning Telescope as a carrier only covers the daytime period.

For practical reasons, another telescope, TSHIPS II, with its own astronomical mounting for independent permanent operation will be installed in a historic building at the Hamburg Observatory. There are plans for another much larger TSHIPS III project; a location for this is currently being inspected on the DESY campus.