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Scientist

Walter Baade

1893–1960 · Astronomy, astrophysics
German astronomer who discovered stellar populations and significantly refined the cosmic distance scale. His work with Fritz Zwicky led to the prediction of neutron stars.

Biography

Born in 1893 in Schröttinghausen, Germany. He studied at the University of Göttingen, receiving his doctorate in 1919. He worked at the Hamburg Observatory, then emigrated to the USA in 1931 and began working at the Mount Wilson Observatory. During the war, he was a German citizen, which restricted his movements but allowed him to observe extensively during blackouts. It was then that he discovered stellar populations. Later he worked at the Palomar Observatory. He received the Catherine Bruce Medal and other awards.

Key discoveries

💡 During World War II, Baade observed stars at night in blacked-out Los Angeles, which allowed him to resolve the central part of the Andromeda Galaxy into stars for the first time. He meticulously verified every hypothesis and once said that he triple-checked his calculations before believing in the doubling of the size of the Universe.
"He compared stars to people, saying they are born, age, and die, and through them one can read the history of the entire Galaxy."
Concepts
metallicitystar formation
Laws
Hubble's law
Scientists
Margaret BurbidgeHans BetheNancy Grace RomanTheodore LymanEmile ClapeyronJames Jeans

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High Energy2012-03-292 minarXiv:1203.6458
Echo of an Explosion in a Quiet Harbor
In the quiet harbor of the Local Bubble, a rarefied cavity of hot gas around the Sun, an explosion recently thundered. A supernova went off tens of parsecs away, and its echo still lingers in the neighborhood, reshaping the cosmic-ray landscape.
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High Energy2025-10-302 minarXiv:2510.26112express
Stellar Explosions as Particle Accelerators of Record Energies
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Stellar2026-01-081 minarXiv:2601.05317express
Fireworks Called Off: Star Shrouded in Smoke
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High Energy2026-01-081 minarXiv:2601.05363express
How One Supernova United Different Types of Explosions
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A Cosmic Blast That Scattered Iron Unevenly
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How Ultrasound Scatters Particles
In a glass of water, ultrasound creates tiny bubbles. They grow and shrink, and sometimes they collapse sharply, like a popping soap bubble, but thousands of times faster. Near these bubbles float small particles — for example, nickel spheres the size of dust motes.
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High Energy2026-01-242 minarXiv:2601.17499express
The Cosmic Web: How a Supernova Explosion Left Its Mark
The James Webb Space Telescope peered into the remnant of the supernova Cassiopeia A — a cloud of gas left behind after a massive star exploded. There, it spotted an intricate web of glowing filaments and a mysterious structure dubbed the 'Green Monster,' featuring nearly circular holes and rings.
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Stellar2026-01-281 minarXiv:2601.20371express
Cosmic Laser Blinks
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Galaxies2026-02-091 minarXiv:2602.08756express
Ancient Explosion Left a Bubble in Space
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High Energy2026-02-091 minarXiv:2602.09175express
Debris from an Exploded Star Changes Course
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Nuclear Experiment2026-02-201 minarXiv:2602.18279express
How a Hot Cloud Bends a Jet
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HEP Phenomenology2026-03-101 minarXiv:2603.09615express
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High Energy2026-03-161 minarXiv:2603.15815express
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Galaxies2026-03-212 minarXiv:2603.20881express
How to Measure the Distance to Supernova Remnants
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High Energy2026-03-221 minarXiv:2603.21307express
The Explosive Letter S: How a Dying Star Draws Loops in Space
In a gas cloud left after a star exploded (called a supernova remnant), astronomers noticed a giant glowing letter S. It was drawn by two jets of superheated material ejected during the cataclysm. These jets didn't just shoot straight out — they slowly spun like a top, which bent their path into curves.
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High Energy2026-03-251 minarXiv:2603.23877express
Supernova Exhaled Carbon Monoxide
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High Energy2026-03-251 minarXiv:2603.24758express
How Carbon and Oxygen Merge: Unraveling Cassiopeia A
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Galaxies2026-03-271 minarXiv:2603.26873express
Patchy Blast: How a Regular Supernova Created Anomalous Stars
Ancient stars, nearly devoid of heavy elements, are like fossilized remnants of the first cosmic flashes. For a long time, the odd ratio of carbon, hydrogen, and helium in three such stars was thought to require a hypernova — an ultra-bright supernova with hundreds of times more energy than a regular one.
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Galaxies2026-03-291 minarXiv:2603.27741express
How AI Watches Over Cosmic Bubbles
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High Energy2026-04-082 minarXiv:2604.07588express
An X-ray Tangle at the Heart of the Milky Way
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High Energy2026-04-092 minarXiv:2604.08686express
Dust Remembers Stellar Explosions
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Galaxies2026-05-132 minarXiv:2605.13231express
Molecular Cradles Under the Shock Wave
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Plasma Physics2026-05-202 minarXiv:2605.21672express
Turbulence from Impact: How Explosions Stir Up Flows
A clap of the hands compresses the air, and it flies outward — the simplest shock. In space, exploding stars play the role of hands: their shock waves sharply compress gas and trigger chaotic mixing — turbulence.
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Stellar2026-05-212 minarXiv:2605.22927express
Stellar Kitchen Before the Bang: Turbulence Instead of a Recipe
A pot of boiling porridge, where instead of grains there are layers of oxygen and silicon, and the fire beneath is about to go out, and the star will collapse in on itself. Until now, astrophysicist cooks have used a simplified recipe: they assumed that bubbles and eddies in the porridge obey one and the same average temperature throughout the depth.
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High Energy2026-06-061 minarXiv:2606.08116express
Squeezed Nebula Outshines the Pulsar: The Secret of Cosmic Bellows
Blacksmith's bellows fan the fire by forcefully pushing out air. In space, the shock wave from a supernova, a concept introduced by Fritz Zwicky, acts like such bellows: it catches up with a giant bubble of charged particles and magnetic fields formed around a spinning neutron star…
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High Energy2026-07-143 minarXiv:2607.12813
Mirror Rift: How Supernova Neutrinos Set Life's Left-Handed Bias
Erwin Schrödinger pondered how life maintains order despite the second law of thermodynamics. He could never have imagined that part of the answer lies hidden in the instability of giant stars.
Amirmasoud Jannat·Soroush Shakeri·Farhad Shahbazi
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High Energy2026-07-223 minarXiv:2607.19705
The Missing Companion of Supernova 1181
On August 6, 1181, Chinese astronomers spotted a new star in the constellation Cassiopeia. It shone for 185 days, slowly fading, and then vanished, leaving only a record in the chronicles. Today, at its location, there is a hot white dwarf — a compressed stellar core with no nuclear reactions, heated to tens of thousands of degrees.
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High Energy2026-07-221 minarXiv:2607.20314express
Why a Star Explosion Is Like a Tug of War
The collapse of a star's core is like compressing a spring: matter falls inward, and a neutron star is born at the center. But the fall is never perfectly smooth. In the boiling outer layers, random eddies transfer angular momentum to the infalling gas, and a disk swirls around the central object. This disk is no calm river. It pulses, strengthening and fading.
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Exoplanets2026-07-242 minarXiv:2607.21948
The Mineral Fingerprint of Star HD 15407A
In 2008, the Spitzer telescope aimed at the star HD 15407A and detected a strong infrared excess. Fifteen years later, in 2023, JWST repeated the measurements. The light from the dust had dimmed by 14%. But the mineral composition of the dust remained the same, like a fingerprint taken in different years.
Shu Wang·Zhuochao Huang·Xiaodian Chen·Junming He·Haomiao Huang
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Stellar2026-08-181 minarXiv:2608.17465express
Clumpy Heart of a Supernova
When a star explodes, its material flies into space. In the supernova remnant SNR 0509-67.5, this material did not spread into a smooth cloud but gathered into separate clumps, like lumps in batter that is quickly stirred. The MUSE telescope in Chile saw these clumps in the faint glow of forbidden iron and calcium lines.
Priyam Das·Ivo Seitenzahl·J. Martin Laming·Gilles Ferrand·Simon J. Murphy·Ashley Ruiter
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High Energy2026-08-232 minarXiv:2608.22374
Two Hands Painting the Sky: Supernova Remnants and Microquasars
The night sky in neutrino light resembles a canvas worked on by two hands. One holds a broad, soft brush: these are supernova remnants, the shells left behind after stellar explosions. The other grips a fine, hard pen — microquasars, binary systems where a black hole twists matter into narrow jets.
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