Yonder, Art·Science at NBI, is located at DARK, an astrophysics research centre at the Niels Bohr Institute, University of Copenhagen.

The Niels Bohr Institute (NBI) is home to DARK and several other internationally recognised research sections spanning physics, astrophysics, geophysics, climate science, and quantum technologies. Current research at NBI ranges from the physics of the early Universe, black holes, and gravitational waves, to quantum communication and quantum optics, as well as ice-core drilling in Antarctica that reveals the Earth’s climate history going back hundreds of thousands of years. Researchers at NBI also study biophysics, complex systems, and particle physics in collaboration with large international consortia such as CERN.

Founded in 1921 by Nobel laureate Niels Bohr, the institute quickly became one of the world’s leading centres for theoretical physics. Bohr’s pioneering work on atomic structure and quantum mechanics attracted generations of scientists to Copenhagen, among them Werner Heisenberg and many others who shaped 20th century physics. Over the past century, NBI has continued this legacy of excellence and international collaboration. Today, it remains a place where fundamental research, education, and interdisciplinary projects come together, fostering innovation across science and society.

DARK brings together scientists working on some of the most fundamental questions in astrophysics and cosmology: the nature of dark matter and dark energy, the formation and evolution of galaxies, cosmic explosions such as supernovae, and the physics of black holes. Researchers combine theoretical modelling, high-performance computing, and observations from state-of-the-art telescopes in space and on the ground. Using facilities such as the James Webb Space Telescope, ESO’s Very Large Telescope, and the ALMA millimeter array, they explore the Universe across X-ray, UV, optical, infrared, millimeter, and radio wavelengths.

The arrow of time is set by entropy — the tendency for energy to spread and disorder to grow. From this principle follow nature’s irreversibilities: stars burn and fade, galaxies evolve, black holes grow. This rise of entropy provides a deep connection between the flow of time and the unfolding history of the Universe.

Researchers: Jens Hjorth, Clara Ferreira Cores, Aman Raju.

Galaxies are dynamic systems that grow and transform across cosmic time. Nearby galaxies reveal the present-day diversity of shapes and structures, while more distant systems show earlier stages and growth. Observations with the James Webb Space Telescope have pushed this view back to the first few hundred million years after the Big Bang, uncovering surprisingly complex and massive galaxies at epochs when the Universe was still very young.

Numerical simulations complement these observations by tracing how galaxies assemble mass, develop spiral arms or central bars, and regulate their star formation through feedback from stars and black holes. Central questions remain about how early galaxies formed stars so rapidly, why some galaxies stop forming stars altogether, and how interactions in clusters or mergers shape their evolution. These investigations connect the evolution of galaxies to both the lives of individual stars and the structure of the Universe on the largest scales, turning galaxies into natural laboratories for studying cosmic history.

Researchers: Jens Hjorth, Cecilia Bacchini, William Baker, Danial Langeroodi

Within the last century, one of the most surprising discoveries in cosmology has changed how the Universe is understood: cosmic expansion is not slowing down under gravity, but accelerating. The mysterious cause of this acceleration is called dark energy — a component that appears to make up about 70 percent of the total energy density of the Universe and acts with a repulsive effect on the largest scales.

Measurements of supernovae, combined with observations of the cosmic microwave background, trace the expansion history over billions of years. Yet, a persistent puzzle remains: measurements of the present-day expansion rate of the Universe — known as the Hubble constant — do not agree with the value inferred from the early Universe within the standard cosmological model. This discrepancy, known as the Hubble tension, may require extensions to the standard model or a fundamental shift in how cosmic history is interpreted. These challenges connect the fate of the Universe to some of the deepest open problems in physics, offering a profound perspective on time, scale, and the limits of human knowledge.

Researchers: Jens Hjorth, Radek Wojtak, Christa Gall, Judit Prat

When stars have exhausted their fuel and end their lives, the most massive explode in supernovae. Their extraordinary brightness makes them visible across vast distances, allowing them to serve as cosmic markers for measuring how space itself expands over time. These explosions scatter elements such as oxygen, silicon, and iron into space, enriching galaxies with the raw material for planets, atmospheres, and life.

Other transient events, such as kilonovae from colliding neutron stars, extend this story by producing heavy elements like gold and platinum while also providing new ways to probe the Universe through gravitational waves. In this way, stellar explosions link the largest questions of cosmology with the origins of the matter that makes us up, showing how death at the level of stars drives creation on cosmic scales.

Researchers: Christa Gall, Aleksandra Lesniewska, Aidan Sedgewick, Aman Raju, Jens Hjorth.

Most of the matter in the Universe is dark — invisible and detectable only through its gravity. Dark matter shapes galaxies, clusters, and the cosmic web, yet its physical nature remains unknown. Research examines the motions of stars, the disruption of stellar streams, and the formation of galaxies to probe this hidden component. Tiny clumps of dark matter may leave imprints on stellar orbits, offering a way to test whether dark matter is cold, warm, or self-interacting. Other studies investigate whether alternative theories of gravity could explain the same phenomena. Dark matter remains one of the great unsolved mysteries of modern science, bridging astrophysics, cosmology, and particle physics.

Researchers: Jens Hjorth, Steen H. Hansen, Sarah Pearson, Jo Verwohlt, Clara Ferreira Cores, Adriana Dropulic, Maya Silverman.

Stellar streams are long, delicate trails of stars created when globular clusters or dwarf galaxies are pulled apart by gravity. Found both in the Milky Way and in nearby galaxies, they preserve a record of galactic growth and interaction. Because they trace the gravitational potential of their host galaxies, tiny distortions in their shape can reveal the presence of dark matter clumps, providing one of the most powerful astrophysical tests of dark matter’s properties. These elegant structures combine fragility with the ability to illuminate the invisible.

Researchers:

Sarah Pearson, Maya Silverman, Adriana Dropulic, Sirui Wu, Julie Kiel Holm.

Black holes are regions of spacetime where gravity is so strong that nothing, not even light, can escape if it comes too close. While stellar-mass black holes form from collapsing stars, supermassive black holes — millions to billions of times the mass of the Sun — reside at the centers of most galaxies, including the Milky Way.

When gas and dust fall toward a supermassive black hole, they heat up and shine across the electromagnetic spectrum, creating what is known as an active galactic nucleus. These luminous central engines can outshine their entire host galaxy and drive powerful winds and jets that help shape how galaxies grow.

Active galactic nuclei are therefore not only extreme laboratories of physics, where gravity and matter reach their limits, but also central players in cosmic evolution. They regulate star formation, influence the distribution of gas, and connect the physics of black holes on small scales to the fate of galaxies on the largest scales.

Researchers: Marianne Vestergaard, Vito Tuhtan, Greg Walsh, Thomas Berlok, Sandra Raimundo.