A universe of possibilities
Put knowledge into perspective, understand new ideas and see the world through fresh eyes: explore our in-depth features. Every article lists its sources. The features are available in German and English and are not breaking-news reports.
Go to the discovery journal220 features · Page 10 of 11
Star-forming regions are often dark in visible light because dust blocks the view. The ALMA observatory studies their millimetre and submillimetre radiation. Its linked antennas reveal cold dust and molecular gas. This makes it possible to explore the regions where stars form and where the raw materials for new planets gather around young stars.
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Observations indicate that the expansion of the universe is not simply slowing down all the time. On large scales, expansion has accelerated in later cosmic epochs. Dark energy is the term for a possible cause within the standard model. Its nature remains an open question and is being investigated using supernovae, galaxy maps and gravitational lensing.
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Dark matter is the name for an as yet unidentified component of matter whose gravitational effects are visible in many places. The movements of galaxies, gravitational lensing and cosmic structures cannot be accounted for by the observed ordinary matter alone. This does not mean that its particles have already been found. Well-measured effects and an unknown nature are two different statements.
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An Earth-sized planet is not automatically a second Earth. Its atmosphere, radiation environment and evolutionary history also matter when assessing potentially life-friendly conditions. Telescopes can study selected gases or a planet’s thermal radiation. Such measurements are valuable, but neither a single molecule nor a location in the habitable zone proves habitability or life.
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Most exoplanets are not photographed as clearly recognisable worlds. Instead, astronomers measure their effect on their host star: regular dimming, tiny changes in velocity or shifts in position. Each method favours particular types of planet. Only by combining them can a conspicuous signal become a reliable description of size, mass and orbit.
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Large masses alter the paths along which light travels through spacetime. If a galaxy or galaxy cluster lies in front of a distant source, distorted arcs, multiple images or amplified signals can arise. Gravitational lenses are therefore both natural observational aids and tools for measuring matter that emits little or no light of its own.
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Gravitational waves are changes in spacetime that propagate outwards. Particularly strong measurable signals arise when compact objects such as black holes or neutron stars orbit one another and merge. Detectors do not measure ordinary sound waves. They compare light paths with extreme precision, providing access to events that may remain invisible in light.
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The James Webb Space Telescope observes mainly infrared light. It uses this to study distant galaxies, dust-shrouded star formation and the atmospheres of selected exoplanets. Its large mirror is only part of its success. Low instrument temperatures, suitable spectrographs and an observing position from which interfering heat can be effectively screened out are just as important.
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A light year is a distance, not a measure of time: it corresponds to approximately 9.46 trillion kilometres. But how do we determine distances that no tape measure can span? Astronomers combine geometric measurements with known relationships involving luminosity. This distance scale stretches from nearby stars to distant galaxies, with its own uncertainties at every stage.
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The cosmic microwave background radiation comes from an epoch when the universe first became largely transparent. Today, its spectrum corresponds to approximately 2.725 kelvin. Tiny differences across the sky contain information about the early density fluctuations. They do not show the Big Bang itself, but an early state of the cosmos, long before the first stars shone.
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Pulsars are rotating neutron stars whose beams of radiation regularly sweep across our line of sight. Their apparent flashing does not mean that the entire star is constantly switching on and off. Particularly stable pulsars serve as precise timekeepers. Their signals help researchers investigate compact matter, galactic movements and even very slow changes in spacetime.
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A rocket does not need to push against air. It accelerates by expelling mass it carries backwards, thereby gaining momentum in the opposite direction. This principle also works in a vacuum. During a launch into orbit, building up a very high sideways velocity is usually harder than simply gaining altitude.
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At the centre of the Milky Way lies Sagittarius A*, a supermassive black hole with approximately four million solar masses. The principal means of determining its mass came not from a look inside, but from the motion of nearby stars. Their orbits also make the galactic centre an exceptional testing ground for gravity.
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A black hole is not an ordinary sphere with a solid surface. Its event horizon bounds a region from which signals can no longer escape. Yet its surroundings can still be studied. Orbiting stars, hot gas and gravitational waves provide different information about mass, motion and extreme spacetime.
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Astronauts do not float because there is no gravity in Earth orbit. Together with their space station, they are in free fall. Their high sideways velocity ensures that they continually miss Earth. This principle also explains why temporary weightlessness is possible in drop towers and research rockets.
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There is no single temperature in space. The cosmic background radiation corresponds to about 2.7 kelvin, while sunlit components can become hot and shielded surfaces very cold. Anyone asking about the temperature of space therefore needs to distinguish between radiation, tenuous gas and a specific object in a vacuum.
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Space debris consists of defunct satellites, rocket remnants and fragments. The danger lies not only in their quantity, but above all in their high speed. Even small pieces can damage active spacecraft. The so-called Kessler effect describes the possibility that collisions generate further debris, making individual orbital regions increasingly difficult to use over the long term.
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The observable universe has a diameter of approximately 93 billion light-years. That does not mean that space as a whole is the same size. The crucial distinction is between an observational limit and an actual edge. Cosmic expansion explains why we can see further than the age of the universe might initially suggest.
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Planets grow in the discs of gas and dust surrounding young stars. Tiny grains must first develop into larger bodies before gravity can substantially accelerate their growth. The transitions between these size ranges are particularly challenging. Observed rings, theoretical models and the diversity of known planetary systems provide different clues.
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Stars form when parts of cold gas clouds become denser under their own gravity. But collapse alone does not explain the entire process. Turbulence, magnetic fields, rotation and radiation from young stars influence how much material gathers together. Only when temperatures inside are sufficiently high does hydrogen fusion begin to provide a sustained source of energy.
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