Illustration: NASA

DTU Space launches new technology on the hunt for neutron stars

Thursday 08 Jun 17


John Leif Jørgensen
Professor and Head of Measurement and Instrumentation
DTU Space
+45 45 25 34 48


Jérôme Chenevez
Associate Professor
DTU Space
+45 45 25 97 03

NICER mission

  • NICER stands for Neutron star Interior Composition Explorer and is a NASA mission in which DTU Space is an international partner.

  • The mission launched on Saturday, 3 June 2017 for the ISS space station from Cape Canaveral in Florida with a Falcon rocket from the private company SpaceX on assignment from NASA. The rocket is one of the new reusable launch systems and has returned to land again after launch. It is thus the first time such an operation has been accomplished commercially by SpaceX for this type of mission.

  • In principle, NICER is an X-ray telescope which will be mounted on top of the ISS. The actual telescope consists of 56 mirror assemblies that function as 'focus lenses' that concentrate incoming X-rays, in the form of photons, from the neutron stars onto silicon detectors.

  • Data are then collected on when and with which energy the photons hit. A GPS system on the ISS keeps track of position and time. At the same time, a navigation system in the form of a modified star camera supplied by DTU Space ensures that the instrument is pointing in the right direction in relation to the neutron stars.

  • In addition to studying neutron stars, NICER will also be used for the first time to test technology that uses signals from the neutron stars in the form of ‘pulses’ of X-rays, photons, to navigate by. Plans are to use this technology in the future for navigation on manned space missions to remote parts of our solar system.

NASA’s recently launched NICER mission—which is to obtain new knowledge about extreme stars in the Milky Way—includes new Danish navigation technology and an exciting scientific task.

DTU has put a solid scientific and technological imprint on the NASA mission which launched for the International Space Station (ISS) from Cape Canaveral in Florida on Saturday, 3 June.

The mission, named NICER, includes a completely new type of X-ray telescope which is to be mounted on the exterior of the ISS, where it will measure X-ray radiation from the remote neutron stars in the Milky Way.

Neutron stars consist of the densest observable matter known to exist in the Universe. On Earth, this would correspond to one teaspoon of the material from a neutron star weighing around 100 billion tonnes.

The next state is a black hole. NICER is, among other things, to help researchers search for answers to how big these stars actually are, what happens in and around them, and how their matter behaves in this extreme state. There are still unresolved issues that the mission is to provide new knowledge about.

“We’ve been working on this project for around six years. Both on developing new technologies for the mission and the ideas which the scientific work with the study of the neutron stars is based on. Of course, we’re very much looking forward to seeing NICER launched and mounted on the ISS so we can get started on the scientific studies,” explains Professor John Leif Jørgensen, DTU Space.

According to plan, NICER is expected to be mounted on the ISS over a course of approx. 10 days and ready to explore space for X-ray radiation.

Key role for DTU

DTU Space is one of the key players in the mission.

“It’s a question of very high-level technological and scientific work solidly anchored at a Danish university which is now on its way to the ISS. It shows that DTU is an internationally preferred partner, and we’re very proud of that,” says Kristian Pedersen, Director of DTU Space, who is in the USA to attend the launch.

DTU Space has the special equipment for navigation—in the form of a modified star camera setup—to ensure that the instrument constantly points in the right direction and is aimed correctly at the small, compact neutron stars far out in the Milky Way. New bespoke elements have been developed for the technology, which are expected to be of great use in future space missions.

In addition, researchers from DTU Space are deeply involved in the ground-breaking scientific work on the measurements of neutron star radiation which NICER is to perform. DTU is guaranteed access to the unique data from the new telescope, which are to enhance our understanding of the distant stars and their significance for the Universe.

“We’ll be working with some of the best data ever collected about neutron stars. This may, among other things, provide new insights into the processes taking place on and in the stars,” says Senior Researcher Jérôme Chenevez, DTU Space.

Among other things, he is going to study a special phenomenon called X-ray bursts which occur on some types of neutron stars. Here, violent thermonuclear explosions take place, and new elements are formed on a neutron star’s surface when ordinary stars orbit around it. The neutron star also draws matter away from ordinary stars.

A jump on board the ISS disturbs the measurements

If an astronaut on board the ISS pushes off from one of the walls, this is enough to set off a movement which causes the space station to move a little bit in its orbit around the Earth, thus disturbing NICER’s focus on the neutron stars.

It must therefore be possible to control the instrument very rapidly and with extremely high precision independently of the space station, so that it is able to point exactly towards the part of the Universe where the radiation from the neutron stars in the form of photons is to be captured. This is done with a new technology developed at DTU Space in the form of a modified star camera.

Over the years, DTU Space has made these star cameras available on a wide range of international missions for both NASA and the European sister organization ESA. But the star camera on the NICER mission is a new and markedly different generation, which has not previously been on a mission.

"We’ll be working with some of the best data ever collected about neutron stars. "
Jérôme Chenevez, DTU Space

Integrating a star camera with an inertial sensor—a combined accelerometer sensor and gyroscope sensor—in a navigation package ensures highly reliable and precise determination of the orientation used to control NICER’s X-ray telescope.

The star camera takes a digital image of the stars and compares it with a map in its computer. In this way, the orientation of the instrument is determined. The accelerometer registers small deviations from a known position, while the gyroscope determines the direction using inertia. Combining these properties results in a unit that can position the X-ray telescope with previously unseen accuracy.

The telescope is mounted on a moveable arm fixed to the space station. The information from the navigation equipment is then used to ensure that the telescope points in the right direction at all times.

“It’s the first time we’ve build this type of navigation package, and we’re now looking forward to testing it in space. Of course, it’s been tried and tested on Earth, and the results have been so good that the technology is already included in a number of future ESA and NASA space missions. So we’ve developed a strong solution from which we expect a great deal in the future,” says John Leif Jørgensen.

Some of the neutron stars that will be studied are called pulsars. They rotate at several thousand rotations per minute and have magnetic fields that are many times stronger than that of the Earth.

The intense activity in neutron stars results, among other things, in X-ray radiation, which can also be captured by NICER. So, in every way, it is some of our Universe’s most extreme phenomena that researchers from DTU and their colleagues will be studying with the NICER mission in the coming years.

Neutron stars: The densest matter that can be observed before it collapses into black holes

  • Over 2,000 neutron stars are known, but there is still a great deal that is not known about them.

  • A neutron star is a collapsed star where the matter has been compressed to an extremely high density gathered in a kind of sphere with a radius of just 10-20 km and with a mass of approx. 1-3 times that of the Sun. Here on Earth, a teaspoonful of material from a neutron star would weigh approx. 100 billion tonnes.

  • The star’s matter is the most compressed material known to exist which can be observed. The next stage of density will be a black hole. Neutron stars thus constitute the limit for the state in which matter can be without collapsing into a black hole.

  • The atoms in a neutron star have been compressed and split apart so that the star consists mainly of subatomic particles in the form of neutrons in various physical states, but possibly also in even more elementary particles such as quarks.

  • Among other things, researchers will attempt to determine the radius and mass of neutron stars more precisely to get a more detailed insight into the processes taking place in and around the star when a mass is exposed to such extreme compression.