What evidence supports the existence of Dark Matter in galaxy clusters?

Fritz Zwicky first postulated dark matter in the 1930s by observing galaxies in the Coma Cluster moving too fast to be gravitationally bound by visible matter. This was later confirmed by gravitational lensing, where the distortion of distant galaxy shapes by foreground clusters reveals a smooth, invisible mass distribution.

How did Vera Rubin's work provide evidence for Dark Matter in individual galaxies?

In the 1970s, Vera Rubin and her collaborators measured the rotation speeds of stars in spiral galaxies like M33. They found that stars in the outer regions orbited much faster than expected based on the visible mass, suggesting that a large, unseen 'dark matter halo' was providing additional gravitational pull.

What are possible candidates for Dark Matter and how are they being searched for?

Dark Matter is thought to be made of new elementary particles called Weakly Interacting Massive Particles (WIMPs). Experiments deep underground look for WIMPs colliding with atomic nuclei, the Large Hadron Collider searches for their production in high-energy collisions, and gamma-ray observatories like Fermi look for gamma rays produced by WIMP annihilation.

Who discovered the expanding universe, and what are common misconceptions about this expansion?

Edwin Hubble discovered the expanding universe in the late 1920s. Misconceptions include thinking the universe has a center or edge, or that galaxies are expanding. The expansion is the increasing distance between galaxies everywhere, likened to raisins in an expanding loaf of bread.

What is the cosmic microwave background radiation and what does it tell us?

The cosmic microwave background (CMB) is an all-sky image of the universe's temperature, currently about 3 degrees above absolute zero. It provides a snapshot of the universe when it was only 380,000 years old, revealing slight temperature fluctuations that evolved into the large-scale structures we see today.

How was the accelerating expansion of the universe discovered, and what is its significance?

In the late 1990s, two teams studying distant Type 1A supernovae found them to be fainter than expected, indicating they were further away than predicted by a slowing expansion. This meant the universe's expansion was speeding up, a discovery that earned a Nobel Prize and implied the existence of dark energy.

What is Dark Energy and what are the leading hypotheses about its nature?

Dark Energy is a mysterious component comprising 70% of the universe, causing its accelerating expansion. It is thought to have negative pressure, causing repulsive gravity. The most conservative hypothesis is that it's the energy of empty space (vacuum energy), though current quantum physics calculations produce an infinitely large value.

How is the Dark Energy Survey (DES) mapping the universe to understand Dark Energy?

The DES uses a 570-megapixel camera on a telescope in Chile to photograph 300 million galaxies over 1/8 of the sky. It employs techniques like studying galaxy clusters, weak gravitational lensing of distant galaxies, measuring large-scale structure, and observing thousands of Type 1A supernovae to reconstruct the universe's expansion and structure growth history, thereby probing dark energy.

What "other fun things" have come out of the Dark Energy Survey besides dark energy and dark matter research?

The DES has discovered 17 new ultra-faint dwarf galaxies orbiting the Milky Way, which are rich in dark matter. It has also helped detect many Trans-Neptunian Objects, providing insights into our solar system's outer regions, and is searching for the hypothetical Planet Nine, whose predicted orbit crosses the survey footprint.

How does the Dark Energy Survey collaborate with gravitational wave observatories like LIGO?

The DES works with LIGO to search for optical counterparts to gravitational wave events. While no optical light was seen for the first black hole merger, future neutron star mergers, which are expected to emit optical light, could be observed by pointing the Dark Energy Camera towards LIGO's detected event regions.

What is the "Big Rip" and is it a likely end-scenario for the universe?

The 'Big Rip' is a hypothetical end-state for the universe if the density of dark energy were to increase with time. In this scenario, the repulsive force of dark energy would eventually overcome all other forces, ripping apart galaxies, stars, planets, and even atoms. However, if dark energy is vacuum energy, the universe would slowly expand, leaving only our local galaxy group visible.

"Probing the Dark Universe" - A Lecture by Dr. Josh Frieman

Fermilab

Science & Technology3 min read106 min video

Jun 6, 2016|7,749,797 views|23,805|5,323

Fermilab Physics Dark Energy Dark Matter Dark Energy Survey mystery

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Key Moments

TL;DR

Explore the universe's composition: 5% ordinary matter, 25% dark matter, 70% dark energy. Learn about dark energy's ongoing mystery and Fermilab's Dark Energy Survey.

Key Insights

The universe is composed of approximately 5% ordinary matter, 25% dark matter, and 70% dark energy.

Dark matter provides the gravitational scaffolding for galaxies and large-scale structures, inferred from galaxy rotation curves and gravitational lensing.

The expansion of the universe is accelerating, a phenomenon attributed to dark energy, which acts as a repulsive force on cosmic scales.

The nature of dark energy remains a profound mystery, with leading hypotheses suggesting it may be the vacuum energy of space.

The Dark Energy Survey (DES) uses a wide-field camera to map millions of galaxies and thousands of supernovae to better understand dark energy and cosmic expansion.

Observational cosmology relies on techniques like gravitational lensing, galaxy surveys, and supernova measurements to probe the universe's structure and evolution.

FUNDAMENTAL FACTS ABOUT THE UNIVERSE

The universe is approximately 13.8 billion years old and vast, with the most distant observable objects nearly 30 billion light-years away. It contains billions of galaxies, which are not uniformly distributed but cluster together in a 'cosmic web.' Nearby galaxies, like the Small and Large Magellanic Clouds, are visible from the Southern Hemisphere, offering a glimpse into the universe's scale and structure.

THE PUZZLE OF DARK MATTER

Evidence for dark matter emerged from observations of galaxy clusters by Fritz Zwicky in the 1930s, who noted galaxies moving too fast to be held by visible matter alone. Later, Vera Rubin's studies of galaxy rotation curves in the 1970s showed stars rotating faster than expected, suggesting unseen mass. Gravitational lensing, the bending of light around massive objects, further confirmed the presence of dark matter in both clusters and individual galaxies, indicating that visible matter is only a small fraction of their total mass.

THE MYSTERY OF DARK ENERGY AND ACCELERATING EXPANSION

Observations in the late 1990s, particularly of Type Ia supernovae, revealed that the universe's expansion is not slowing down due to gravity, but is in fact accelerating. This led to the concept of dark energy, a mysterious component with repulsive gravitational properties that makes up about 70% of the universe. Unlike dark matter and ordinary matter, dark energy's density appears to remain constant as the universe expands. Its nature is unknown, with vacuum energy being a leading, albeit problematic, hypothesis.

THE COMPOSITION OF THE UNIVERSE

Current cosmological models suggest that ordinary matter, the stuff atoms are made of, constitutes only about 5% of the universe. Dark matter, which interacts gravitationally but not electromagnetically, makes up roughly 25%. The dominant component, at about 70%, is dark energy, responsible for the accelerated expansion. The relative proportions of these components have changed over cosmic history, with dark matter being more dominant in the early universe, driving structure formation.

THE DARK ENERGY SURVEY (DES)

The Dark Energy Survey, utilizing a specialized camera on a telescope in Chile, aims to map a significant portion of the sky. By observing hundreds of millions of galaxies and thousands of supernovae, DES employs techniques like weak gravitational lensing, galaxy clustering, and supernova measurements to constrain the properties of dark energy and understand the history of cosmic expansion and structure formation. The survey involves a large international collaboration of scientists.

EXPLORING THE COSMOS AND BEYOND

The DES data, while primarily aimed at dark energy research, has also yielded discoveries in other areas, including new dwarf galaxies in our cosmic neighborhood, potential insights into hypothetical structures like 'Planet Nine,' and the search for optical counterparts to gravitational wave events detected by LIGO. These ancillary studies highlight the broad scientific impact of large-scale sky surveys.

Mentioned in This Episode

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●Concepts

●People Referenced

Cosmic Composition Evolution

Data extracted from this episode

Time after Big Bang	Dark Energy (%)	Dark Matter (%)	Ordinary Matter (%)
Today	70	25	5
9.5 Billion Years	50	43	7
1 Billion Years	1	84	15

Common Questions

The universe is estimated to be 13.8 billion years old. This age is determined by observing old stars in our galaxy, such as those in globular clusters like Omega Centauri, and through observations of the cosmic microwave background radiation.

Mentioned in this video

conceptNGC 1703

A foreground galaxy mentioned with a more distant cluster behind it, illustrating galaxy clustering.

personJohn Grunsfeld

An astronomer and University of Chicago graduate who brought Edwin Hubble's championship basketball to the Space Shuttle during a Hubble Space Telescope refurbishment mission.

conceptNGC 1672

A large spiral galaxy mentioned as an example of galaxies existing in groups.

personAndre Sals

Introduced the speaker Dr. Josh Frieman and is part of the Arts and Lecture Series committee at Fermilab.

toolPalomar 48-inch Telescope

A telescope partially pictured with Edwin Hubble, illustrating observational astronomy history.

organizationCerro Tololo Inter-American Observatory

The observatory in the northern Andes mountains of Northern Chile where the Blanco Telescope is located and operated.

organizationNational Optical Astronomy Observatory

The organization that operates the Blanco Telescope.

conceptNGC 1365

A prominent spiral galaxy within the Forax Cluster, used as an example of an image from the Dark Energy Camera.

conceptNGC 1566

A specific galaxy mentioned as an example of images taken by the Dark Energy Camera.

conceptEinstein's theory of relativity

The theory by Albert Einstein that redefined gravity as the curvature of SpaceTime, used to explain gravitational lensing.

conceptChandrasekhar Mass

The maximum stable mass for a white dwarf star, approximately 1.4 times the mass of the Sun, beyond which it will explode as a Type 1A supernova.

conceptPlanet Nine

A hypothetical new planet with about 10 times the mass of Earth, whose existence is postulated due to the regular orbits of Trans-Neptunian Objects, with its likely orbit crossing the Dark Energy Survey's footprint.

personMordehai Milgrom

An Israeli physicist credited with developing the theory of Modified Newtonian Dynamics (MOND) as an alternative to dark matter.

personJennifer Gunn

A flutist performing in the Gallery Chamber Series mentioned during the introductory remarks.

organizationSloan Digital Sky Survey Supernova Survey

A previous project led by Dr. Frieman that discovered over 500 supernovae for cosmic study.

conceptSupernova 1A

A specific type of supernova caused by the thermonuclear explosion of a white dwarf star exceeding the Chandrasekhar Mass, used as 'standard candles' to measure cosmic distances.

conceptNGC 1512

A relatively nearby spiral galaxy that is about 38 million light-years away, imaged by the Dark Energy Camera.

conceptComet Lovejoy

A bright comet that happened to pass through the field of view of the Dark Energy Camera while an image was being taken.

personPhil Mo

From Oregon State University, scheduled to give a talk on climate change at Fermilab.

organizationStars of Dance Chicago

A group of local dance troupes scheduled to perform at Fermilab.

conceptM33 Galaxy

A spiral galaxy similar to the Milky Way, studied by Vera Rubin to measure star rotation speeds, providing evidence for dark matter.

personTim Monroe

A flutist performing in the Gallery Chamber Series mentioned during the introductory remarks.

personJosh Frieman

Professor of Astronomy and Astrophysics at the University of Chicago, Senior Scientist at Fermilab, and founder/director of the Dark Energy Survey.

conceptNGC 253

A specific galaxy mentioned as an example of images taken by the Dark Energy Camera.

productPlank Satellite

A satellite that captured the all-sky image of the cosmic microwave background radiation, providing a snapshot of the early universe.

organizationDepartment of Energy (DoE)

A United States government department that supports the Dark Energy Survey.

toolBlanco Telescope

A telescope located on Cerro Tololo in Chile, where the Dark Energy Camera is installed.

conceptOort Cloud

A hypothetical vast cloud of icy planetesimals at the outermost reaches of the solar system.

conceptOrion Nebula

A beautiful image taken with the Dark Energy Camera, though unrelated to cosmology or the survey's primary goals.

conceptWeakly Interacting Massive Particle (WIMP)

A hypothetical new elementary particle, 10 to 100 times the mass of a proton, proposed as a candidate for dark matter due to its weak interaction with ordinary matter and light.

conceptForax Cluster

A nearby cluster of galaxies, images of which were among the first taken by the Dark Energy Camera in 2012.

conceptSadna

An interesting planet-like object discovered years ago in the outer solar system, mentioned in the context of Trans-Neptunian Objects.

locationComa Cluster