Discovering a Runaway Universe - NASA Science

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Nearly a century after astronomer Edwin Hubble discovered that the universe is expanding, the telescope named in his honor refined his distance measurements. Astronomers use the Hubble telescope to measure distances by comparing the brightness of a known object in our galaxy (like a star or a supernova) to that of similar objects in a distant galaxy. They then couple those distances with the best galaxy-velocity measurements obtained from other telescopes. After more than three decades of observations, teams using Hubble’s extraordinary capabilities have measured the expansion rate to a precision of just over 1%, about eight times more precise than they originally anticipated! This value for the Hubble Constant puts the age of the universe at about 13.8 billion years old. However, there is a twist… Our universe is not only growing, but that expansion rate is accelerating.

Hubble observations, along with those of ground-based observatories, surprised astronomers by revealing that the universe is not just expanding but accelerating – a discovery that won the 2011 Nobel Prize in Physics. Astronomers use stars like Type Ia supernovae and Cepheid variables to determine astronomical distances because these types of stars have well-known brightness curves. Once they know the galaxy’s distance and how fast it is moving away from us, they can calculate the Hubble Constant.

Ground-based image of the Andromeda Galaxy stretches from lower left to upper right. A white arrow points to the location of the Hubble observations. Above the galaxy are four boxes containing Hubble images of the variable star at different luminosities.

Astronomers use cyclical changes in the brightness of Cepheid stars to determine astronomical distances. The arrow points to a Cepheid star in the Andromeda galaxy observed by Hubble (inset boxes).

NASA, ESA, Hubble Heritage Team (STScI/AURA), R. Gendler

When the Hubble Space Telescope launched in 1990, one of its main goals was to measure the rate at which our universe is expanding.
NASA; Producer & Director: James Leigh

To improve the precision of the Hubble constant, astronomers analyzed Hubble data from 19 galaxies, including NGC 1015. This color-composite of NGC 1015 holds yellow circles that represent the location of Cepheid variable stars. Cepheids are excellent beacons for measuring accurate distances to nearby galaxies because their pulsation rate closely matches their intrinsic brightness.

A grid of 36 galaxy images, 4 rows of 9 images each.

This collection of 36 Hubble images features galaxies that are all hosts to both Cepheid variables and supernovae. These two celestial phenomena are both crucial tools used by astronomers to determine astronomical distance, and have been used to refine our measurement of the Hubble constant, the expansion rate of the universe. The galaxies shown in this photo (from top row, left to bottom row, right) are: NGC 7541, NGC 3021, NGC 5643, NGC 3254, NGC 3147, NGC 105, NGC 2608, NGC 3583, NGC 3147, Mrk 1337, NGC 5861, NGC 2525, NGC 1015, UGC 9391, NGC 691, NGC 7678, NGC 2442, NGC 5468, NGC 5917, NGC 4639, NGC 3972, The Antennae Galaxies, NGC 5584, M106, NGC 7250, NGC 3370, NGC 5728, NGC 4424, NGC 1559, NGC 3982, NGC 1448, NGC 4680, M101, NGC 1365, NGC 7329, and NGC 3447.

NASA, ESA, Adam G. Riess (STScI, JHU)

Type Ia supernovae are also good indicators because they all peak at the same brightness. Astronomers use the difference between its intrinsic peak brightness and how bright it appears to calculate how far away the supernova must be. The small cross-shape near the top of the galaxy denotes the location of a Type Ia supernova.

Comparing both Cepheids and Type Ia supernovae in nearby galaxies allows astronomers to calibrate the brightness of Type Ia supernovae in more distant galaxies, which helps refine their overall measurements of the Hubble Constant.

Two galaxies with annotations

NGC 1015 is 118 million light-years from Earth.

NASA, ESA, Adam G. Riess (STScI, JHU)

A portion of the Hubble Deep Field. Two observations of the same part of the sky. 1995 reels a bright star that is no longer there in the 2002 observation. This animated gif cycles between the two images making the supernova appear to blink on and off.

Certain supernovas have a characteristic maximum brightness that can be used to calculate their distances from Earth. Refining celestial distances enables astronomers to better calculate the expansion rate of the universe. The arrow points to a distant supernova discovered in an area of the sky first imaged in 1995 called the Hubble Deep Field. Astronomers found the supernova when they targeted the same area of sky again in 2002 and saw a change.

NASA and J. Blakeslee (JHU)

Hubble (WFC3) & Webb (NIRCam) Image of NGC 5468

In 2023, to try to eliminate the possibility of measurement errors, researchers used NASA’s James Webb Space Telescope to test their Hubble results. Those observations confirmed Hubble’s results, leading some scientists to suggest that something else – not measurement errors – is influencing the expansion rate.
Many scientists believe an invisible force, called “dark energy,” causes this acceleration. We can think of dark energy as an “antigravity” or repelling force that pushes galaxies apart by stretching space at an increasing pace. Although current technology does not allow us to directly measure dark energy, we can characterize it by observing its effect on normal matter in the visible universe. From these observations, scientists estimate that dark energy is about 68%, dark matter is about 27%, while normal matter and energy are only about 5% of the entire universe. By studying how dark energy behaves over time, astronomers hope to gain a better understanding of what it is and how it might affect the future of the cosmos.

NASA’s Webb, Hubble Telescopes Affirm Universe’s Expansion Rate, Puzzle Persists

This image of NGC 5468, a galaxy located about 130 million light-years from Earth, combines data from the Hubble and Webb space telescopes. This is the farthest galaxy in which Hubble has identified Cepheid variable stars. These are important milepost markers for measuring the expansion rate of the universe. The distance calculated from Cepheids has been cross-correlated with a type Ia supernova in the galaxy. Type Ia supernovae are so bright they are used to measure cosmic distances far beyond the range of the Cepheids, extending measurements of the universe’s expansion rate deeper into space.
NASA, ESA, CSA, STScI, Adam G. Riess (JHU, STScI)

Dark energy is just one of the mysteries Hubble is trying to uncover.
NASA; Producer & Director: James Leigh

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Image is filled with distant galaxies in colors of yellow-gold, red, blue, white. Lower left holds a face on spiral galaxy.

Hubble Finds Universe Expanding Faster Than Expected

Astronomers using NASA’s Hubble Space Telescope have discovered that the universe is expanding 5 percent to 9 percent faster than expected.

A grid of 36 galaxy images, 4 rows of 9 images each.

New Milestone in Mystery of Universe’s Expansion Rate

Completing a nearly 30-year marathon, NASA’s Hubble Space Telescope has calibrated more than 40 “milepost markers” of space and time to help scientists precisely measure the expansion rate of the universe – a quest with a plot twist.

four images of quasars, each appearing duplicated due to effects of gravitational lensing

Cosmic Magnifying Glasses Yield Independent Measure of Universe’s Expansion

A team of astronomers using NASA’s Hubble Space Telescope has measured the universe’s expansion rate using a technique that is completely independent of any previous method.

diagram depicting means of measuring Hubble constant

New Measure of Hubble Constant Adds to Mystery of Universe’s Expansion Rate

Astronomers have made a new measurement of how fast the universe is expanding, using an entirely different kind of star than previous endeavors. The revised measurement, falls in the center of a hotly debated question in astrophysics that may lead to a new interpretation of the universe’s fundamental properties.

Hubble Science Highlights

Discover the breadth and depth of Hubble's exciting discoveries!

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Hubble image left to right: Jupiter, Uranus, Saturn, Neptune

Studying the Planets and Moons

Hubble’s systematic observations chart the ever-changing environments of our solar system’s planets and their moons.

animation of a binary asteroid with a shifting tail

Tracking Evolution in the Asteroid Belt

These conglomerates of rock and ice may hold clues to the early solar system.

Three views of Pluto. Three mottled circles in colors of yellow, grey, rusty-orange, and black.

Uncovering Icy Objects in the Kuiper Belt

Hubble’s discoveries helped NASA plan the New Horizon spacecraft’s flyby of Pluto and beyond.

The Mystic Mountain is seen as a chaotic pillar of colorful gas and dust, narrowing toward the top of the image. The dust and gas is mostly yellow, brown, and orange, all jutting against a hazy purple and blue background with a few pink stars.

Exploring the Birth of Stars

Seeing ultraviolet, visible, and near-infrared light helps Hubble uncover the mysteries of star formation.

Hubble image of the Crab Nebula

The Death Throes of Stars

When stars die, they throw off their outer layers, creating the clouds that birth new stars.

Thirty proplyds in a 6 by 5 grid. Each one is unique. Some look like tadpoles, others like bright points in a cloudy disk.

Finding Planetary Construction Zones

Hubble’s sensitivity uncovers the seeds of planets in enormous disks of gas and dust around stars.

Artist's impression of the ten hot Jupiter exoplanets. Two rows of exoplanet illustrations. There are 5 planets of varying sizes, colors, and atmospheric features in each row.

Recognizing Worlds Beyond Our Sun

Hubble can detect and measure the basic organic components for life on planets orbiting other stars.

Hubble view of an expanding halo of light around star v838 monocerotis

Seeing Light Echoes

Like ripples on a pond, pulses of light reverberate through cosmic clouds forming echoes of light.

Hubble Ultra Deep Field image

Tracing the Growth of Galaxies

Hubble’s Deep Field observations are instrumental in tracing the growth of galaxies.

Comma shaped curved cloud of gases in bright white edged with bright-pink star forming regions, and threaded with rusty-brown tendrils of dust at center and throughout the comma shaped merger. All set against the black of deep space.

Galaxy Details and Mergers

Galaxies evolve through gravitational interaction with their neighbors, creating a menagerie of forms.

Computer simulation of a supermassive black hole at the core of a galaxy. Center is a black circle. Surrounding the black circle are arcs of red, blue, orange, and white. Further out from the circle are blotches of red, blue, orange, and white representing celestial objects.

Monster Black Holes are Everywhere

Supermassive black holes lie at the heart of nearly every galaxy.

Six Hubble images in a grid of three across and two down. Each is a gamma-ray burst in a host galaxy. The images are orange-red and white with hints of yellow.

Homing in on Cosmic Explosions

Hubble helps astronomers better understand and define some of the largest explosions in the universe.

A field of galaxies along with the curved arcs of gravitationally lensed galaxies.

Focusing in on Gravitational Lenses

Gravitational lenses are ‘Nature’s Boost’, expanding our view deeper into space and farther back in time.

A cluster of galaxies fills the frame. A purple glow around the largest concentrations of galaxies indicates the distribution of dark matter.

Shining a Light on Dark Matter

The gravitational pull of dark matter guides the formation of everything we can see in the universe.

Top: Three views going back in time show slices of the cosmos. Bottom: A computer simulated, 3-D map of the distribution of dark matter.

Mapping the Cosmic Web

Filaments and sheets of matter create an interconnected web that forms the large-scale structure of the universe.