Josh Simon uses observations of nearby galaxies to study problems related to dark matter, chemical evolution, star formation, and the process of galaxy evolution.

In one area he looks at peculiarly dark galaxies. Interestingly, some galaxies are so dark they glow with the light of just a few hundred Suns. Simon and colleagues have determined that a tiny, very dim galaxy orbiting the Milky Way, called Segue 1, is the darkest galaxy ever found and has the highest dark matter density ever found. His team has also laid to rest a debate about whether Segue 1 really is a galaxy or a globular cluster—a smaller group of stars that lacks dark matter. Their findings make Segue 1 a promising laboratory to study dark matter, particularly the possibility that dark matter could be seen for the first time via a detection of gamma rays emanating from colliding dark matter particles.

Dark matter is the mysterious nonluminous material that makes up about most of the universe.  Dark energy is a mysterious repulsive force. Together they make up  about 95% of the universe. The rest--all observable matter--adds up to less than 5% of the universe.  Nearby dwarf galaxies have the highest measured densities of dark matter, making them ideal for dark matter studies, but that proximity also has a downside. Star systems so close to the massive Milky Way are subject to the acceleration of their stars by our galaxy’s tidal forces, an effect that can mimic the presence of dark matter. The lack of bright stars in dim dwarfs also makes it difficult to measure the velocities of enough stars for sufficient certainty. Simon and company overcame these hurdles with a comprehensive program that measured and analyzed the speed and chemistry of 397 stars in the vicinity of Segue 1.

 A major difference between galaxies and globular clusters--spherical collections of stars that are gravitationally bound--is that the stars in galaxies contain widely varying amounts of iron and other heavy elements, while stars in clusters do not. The new observations revealed that some Segue 1 stars have 50 times less iron than others in the galaxy, demonstrating conclusively that Segue 1 cannot be a globular cluster.

In collaboration with astronomers, Simon also showed that the high speeds of the Segue 1 stars are not caused by invisible binary companion stars, firming up the estimates of the amount of dark matter in the galaxy. Ongoing observations with NASA’s Fermi Gamma-ray Space Telescope are searching for signals from Segue 1 and other dwarfs, which would provide astronomers with concrete proof that their dark matter theories are on the right track\

Simon received his B.S. in physics from Stanford University and his M.A. and Ph. D. in astrophysics from UC-Berkeley. He was a postdoctoral scholar at Caltech from 2005-2008 and  the Vera Rubin Fellow at Carnegie from  2008 to 2010. For more information see http://obs.carnegiescience.edu/users/jsimon

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Illustration by James Josephides, courtesy of Swinburne Astronomy Productions.
November 12, 2019

Pasadena, CA—A star traveling at ultrafast speeds after being ejected by the supermassive black hole at the heart of our galaxy was spotted by an international team of astronomers including Carnegie’s Ting Li and Alex Ji. Their work is published by Monthly Notices of the Royal Astronomical Society. Hurtling at the blistering speed of 6 million kilometers per hour, the star is moving so fast that it will leave the Milky Way and head into intergalactic space.

Called S5-HVS1, the star was discovered in the Grus, or Crane, constellation by lead author Sergey Koposov of Carnegie Mellon University as part of the Southern Stellar Stream Spectroscopic Survey led by Carnegie

Ancient gas cloud courtesy of the Max Planck Society.
November 8, 2019

Washington, DC— The discovery of a 13 billion-year-old cosmic cloud of gas enabled a team of Carnegie astronomers to perform the earliest-ever measurement of how the universe was enriched with a diversity of chemical elements.  Their findings reveal that the first generation of stars formed more quickly than previously thought. The research, led by recent Carnegie-Princeton fellow Eduardo Bañados and including Carnegie’s Michael Rauch and Tom Cooper, is published by The Astrophysical Journal.

The Big Bang started the universe as a hot, murky soup of extremely energetic particles that was rapidly expanding.  As this material spread out, it cooled,

Patrick McCarthy courtesy of GMTO
October 1, 2019

Pasadena, CA—Carnegie astronomer and Vice President of the Giant Magellan Telescope (GMT), Patrick McCarthy, has been appointed as the first Director of the National Science Foundation’s newly formed National Optical-Infrared Astronomy Research Laboratory (NSF’s OIR Lab).

McCarthy has been a member of the GMT project since its inception 15 years ago, helping to bring it from a sketch on a napkin to a 100-plus person organization with 12 U.S. and international partners. In 2008, 20 years into his tenure at Carnegie, McCarthy officially expanded his role when he accepted his current leadership position at GMT.

Working with then-Carnegie Observatories

lustración por Robin Dienel, cortesía de Carnegie Institution for Science.
September 26, 2019

Washington, DC—El satélite Transiting Exoplanet Survey Satellite (TESS) de la NASA ha observado por primera vez las secuelas de una estrella que fue violentamente desgarrada por un agujero negro supermasivo. El haber capturado en pleno desarrollo un evento tan poco común ayudará a los astrónomos a entender estos misteriosos fenómenos.

Las observaciones fueron publicadas en la revista científica The Astrophysical Journal y el estudio fue liderado por el astrónomo de la Institución Carnegie, Thomas Holoien. Holoien es uno de los miembros fundadores de la red internacional de telescopios que realizó el

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The fund supports a postdoctoral fellowship in astronomy that rotates between the Carnegie Science departments of Terrestrial Magnetism in Washington, D.C., and the Observatories in Pasadena California. 

The Earthbound Planet Search Program has discovered hundreds of planets orbiting nearby stars using telescopes at Lick Observatory, Keck Observatory, the Anglo-Australian Observatory, Carnegie's Las Campanas Observatory, and the ESO Paranal Observatory.  Our multi-national team has been collecting data for 30 years, using the Precision Doppler technique.  Highlights of this program include the detection of five of the first six exoplanets, the first eccentric planet, the first multiple planet system, the first sub-Saturn mass planet, the first sub-Neptune mass planet, the first terrestrial mass planet, and the first transit planet.Over the course of 30 years we have

The Giant Magellan Telescope will be one member of the next class of super giant earth-based telescopes that promises to revolutionize our view and understanding of the universe. It will be constructed in the Las Campanas Observatory in Chile. Commissioning of the telescope is scheduled to begin in 2021.

The GMT has a unique design that offers several advantages. It is a segmented mirror telescope that employs seven of today’s largest stiff monolith mirrors as segments. Six off-axis 8.4 meter or 27-foot segments surround a central on-axis segment, forming a single optical surface 24.5 meters, or 80 feet, in diameter with a total collecting area of 368 square meters. The GMT

Along with Alycia Weinberger and Ian Thompson, Alan Boss has been running the Carnegie Astrometric Planet Search (CAPS) program, which searches for extrasolar planets by the astrometric method, where the planet's presence is detected indirectly through the wobble of the host star around the center of mass of the system. With over eight years of CAPSCam data, they are beginning to see likely true astrometric wobbles beginning to appear. The CAPSCam planet search effort is on the verge of yielding a harvest of astrometrically discovered planets, as well as accurate parallactic distances to many young stars and M dwarfs. For more see  http://instrumentation.obs.carnegiescience.edu/

Evolutionary geneticist Moises Exposito-Alonso joined the Department of Plant Biology as a staff associate in September 2019. He investigates whether and how plants will evolve to keep pace with climate change by conducting large-scale ecological and genome sequencing experiments. He also develops computational methods to derive fundamental principles of evolution, such as how fast natural populations acquire new mutations and how past climates shaped continental-scale biodiversity patterns. His goal is to use these first principles and computational approaches to forecast evolutionary outcomes of populations under climate change to anticipate potential future

Staff Associate Kamena Kostova joined the Department of Embryology in November 2018. She studies ribosomes, the factory-like structures inside cells that produce proteins. Scientists have known about ribosome structure, function, and biogenesis for some time. But, a major unanswered question is how cells monitor the integrity of the ribosome itself. Problems with ribosomes have been associated with diseases including neurodegeneration and cancer. The Kostova lab investigates the fundamental question of how cells respond when their ribosomes break down using mass spectrometry, functional genomics methods, and CRISPR genome editing.

Kostova received a B.S. in Biology from the

Sally June Tracy applies cutting-edge experimental and analytical techniques to understand the fundamental physical behavior of materials at extreme conditions. She uses dynamic compression techniques with high-flux X-ray sources to probe the structural changes and phase transitions in materials at conditions that mimic impacts and the interiors of terrestrial and exoplanets. She is also an expert in nuclear resonant scattering and synchrotron X-ray diffraction. She uses these techniques to understand novel behavior at the electronic level.  Tracy received her Ph.D. from the California Institute of

The Ludington lab investigates complex ecological dynamics from microbial community interactions using the fruit fly  Drosophila melanogaster. The fruit fly gut carries numerous microbial species, which can be cultured in the lab. The goal is to understand the gut ecology and how it relates to host health, among other questions, by taking advantage of the fast time-scale and ease of studying the fruit fly in controlled experiments.