Cosmic Journeys – Hubble: Universe in Motion


Not since Galileo invented the telescope,
over 400 years ago, has our view of the universe been so transformed. In April 1990, astronauts stationed the Hubble
Space Telescope in orbit… above the blurring effects of Earth’s atmosphere. It returned scenes of unprecedented beauty. As well as clear, sharp images of a dynamic,
changing universe. Stars… Planets… Galaxies… each evolving in time, from birth…
to dissipation… and death. This portrait of a Universe in Motion… is
Hubble’s enduring legacy. The Hubble Space Telescope is now regarded
as one of most revolutionary scientific instruments ever built. While not the only telescope launched into
orbit, it has surely been the most versatile. Spacewalking astronauts returned four times
to upgrade its instruments to newer and more powerful technologies. As a result, Hubble has been able to probe
the life cycle of stars, from their birth in nurseries of dust-laden clouds of gas… All the way to their final farewell: as delicate
nebulae, slowly blown into space… or as titanic supernova explosions that outshine
their host galaxies. Hubble has peered into the breeding grounds
of new solar systems: dusty discs around newborn stars that may condense into planets. And it has transported us into the billions
of galaxies that spread out across the depths of time and space. One of the most photogenic galaxies is a grand
spiral called M74, located about 32 million light years from Earth. Amateur astronomers have long known it as
the “phantom galaxy,” because of its low surface brightness. Hubble astronomers, on the other hand, saw
spiral arms laced with delicate tendrils of dust silhouetted against bright ribbons of
stars. These spiral arms are not like spokes on a
wheel. They are density waves that move around the galaxy compressing gas… and stimulating
the birth of vast waves of new stars. Using Hubble, astronomers are uncovering fascinating
details within galaxies they once considered featureless and bland. NGC 1132 is an immense ball of stars some
320 million light years away. Astronomers have concluded that this giant
is the product of a gravitational feeding frenzy. Hubble showed that its surroundings are dotted
with dense clusters of stars. They are what’s left of galaxies that were swallowed by 1132. How galaxies grow and evolve over time is
an enduring mystery that Hubble astronomers have sought to unravel. The first galaxies are thought to have formed
out of clumps of gas in the early Universe. These proto-galaxies came together to form
larger and larger galaxies. Such galactic mergers may play out over hundreds
of millions of years. Hubble has shown that it is an elegant waltz of stars and gas…
choreographed by gravity on a grand cosmic stage. As the galaxies pass each other, their gravity
pulls stars and gas into the space between them, building vast luminous bridges stretching
tens of thousands of light years. As the galaxies fall together again, long
streams of gas and dust, known as tidal tails, wrap around their disrupted shapes. As the galaxy cores approach each other, the
gas and dust clouds that envelop them can be dramatically accelerated. This results
in shockwaves that ripple through interstellar clouds…. Setting off bursts of star formation
that appear as brilliant blue knots. Gravity is not the only force that can tear
a galaxy apart. Hubble spotted a spiral galaxy plowing through
a cluster of galaxies. There, it is has encountered a vast cloud of superheated gas. Drag from this cloud is stripping away gas
from the galaxy, creating tattered threads and blue tendrils. It’s also pulling away streams of murky
dust, as shown by the dark brown tangled region around the galaxy’s center. When Hubble observations are combined with
X-ray images, a bright, extended fog can be seen enveloping the galaxy and streaming off
into space. In the end, this encounter will leave the
galaxy with very little gas, and almost no chance of forming any new stars. Galaxy collisions are not always destructive.
Take the case of Centaurus A, 32 million light years from Earth. Shockwaves produced by a collision have sparked
an intense round of star formation, as seen in the red patches visible here. There is something else about Centaurus A
that stands out. Using radio and x-ray telescopes, astronomers have spotted powerful jets blasting
out of its center… and broad plumes of matter racing far beyond the galaxy. Where is all that energy coming from? Answering
that question has become a major focus of Hubble observations since the day it was launched. Astronomers had long noticed that the centers
of large galaxies are unusually bright. They speculated that there must be some kind of
massive object lurking there. Could these objects be dense collections of
stars? Or are they a breed of supermassive black holes, millions or even billions of
times the mass of our sun? Hubble’s search for the answer began in
the center of a giant nearby galaxy, M87. Astronomers saw that its color was not quite
the same on both sides. One side was shifted towards blue and the other towards red, a
hint that it must be rotating very quickly. This is because the wavelength of light is
changed by the motion of whatever is emitting it. This is also known as the Doppler effect. Think about how the pitch of a train whistle
drops as it races past. Similarly, if something in space is moving
towards you, the wavelength of its light gets squashed, making it appear bluer. If the object
is moving away, its light gets stretched, making it redder. By measuring how much the colors had shifted
from one side of the disk to the other, astronomers were able to determine its speed of rotation.
It turned out that this disk was spinning at a rate of hundreds of kilometers per second. Astronomers concluded that an object must
be lurking in its center that’s at least 4 billion times the mass of our Sun – a
supermassive black hole. This was a key piece of evidence in the discovery
that supermassive black holes occupy the centers of most, if not all, large galaxies, including
our own Milky Way. Back in the early 20th century, the young
astronomer Edwin Hubble joined a larger quest to understand the scales of time and distance
that define our universe. To make his measurements, he observed stars
in the nearby Andromeda galaxy, just 2.5 million light years away. His namesake, the Hubble Space Telescope,
has extended those measurements to the far limits of time and space. In its legendary Deep Field images, Hubble
stared into seemingly blank regions of sky, revealing thousands of faint galaxies from
the early days of the universe. These blotchy collections of stars are infant
galaxies. Over the 10 billion years their light has traveled to reach us, some may have
evolved into galaxies that resemble our own… With a supermassive black hole in its center…
spiral arms… exploding stars… solar systems… planets… and perhaps even life. Hubble has shown that our Milky Way galaxy
is a dynamic cosmic laboratory. Some of its most striking and beautiful images
are giant structures known as nebulae. This one is nicknamed Horsehead, after its
clear and curiously familiar shape. Rising from a sea of gas and dust, this so-called
dark nebula is a cold, dark, dusty cloud set against a background of glowing gas. Then there’s the famed Eagle Nebula, nicknamed
the Pillars of Creation. A group of hot young stars is scouring these luminous towers with
fierce winds of energetic particles. Dense pockets of gas resist these winds. Within
them, are cocoons of gas and dust, where new stars are being born. You can see the same process underway in the
Monkeyhead Nebula, about 6400 light-years away in the constellation of Orion. The Monkeyhead is a stellar nursery with all
the ingredients needed for star formation. Its peaceful beauty masks the violent events
within it. In places where stars are able to form at
high rates, Hubble astronomers have zeroed in on the moment of birth. One team has been collecting high-resolution
Hubble images of energetic jets of matter being shot from newborn stars. Unlike most astronomical phenomena, which
can appear motionless over centuries of time, these jets visibly change on human timescales. Using Hubble, astronomers can see knots of
gas brightening and dimming. This shows that these jets are not being launched in a steady
stream. Rather, they are racing out sporadically in
clumps. The irregular structure of these jets is likely caused by material that periodically
falls onto an infant star. This image shows how violent the end stages
of star formation can be. In the constellation of Cygnus, a few thousand
light-years away, lies a compact star-forming region called S106. The beautiful colors of this nebula mask the
violent events taking place within. A young star, named S106 IR, is being born
at the heart of the nebula. In the final stages of its formation, the star is ejecting material
at high speed, disrupting surrounding clouds of gas and dust. 3D visualizations show the extent to which
the star has carved its surroundings into a complex shape, including hollow cavities. At the outer edges of these cavities, the
gas has been compressed into shock fronts. The material spewing off the star not only
gives the cloud its hourglass shape, it is heating it up to temperatures of 10,000 degrees
Celsius. The star’s radiation excites the gas, making
it glow like a fluorescent light bulb. A star is born when pressure and heat in its
core causes hydrogen gas to undergo nuclear fusion. The heat generated by this process
pushes outward… countering the inward pull of gravity. From the violence of their birth, most stars
spend their lives shining in relative peace, gradually using up the hydrogen fuel that
makes up their cores. Smaller, cooler stars are incredibly efficient.
A red dwarf, with 10% the mass of our sun, can burn for ten trillion years… almost
a thousand times the current age of the universe. By comparison, larger, hotter stars like our
sun burn more quickly. At about 5 billion years old, our own sun has gone through half
its expected lifespan. By observing stars similar to the Sun, scientists
now have a good idea of what will happen to our Solar System in the distant future. The sun will grow steadily hotter… causing
it to swell into a so-called red giant. When the Sun does this, it will destroy the inner
planets of the Solar System. Next, the outer layers will puff out, forming
a dense cloud of gas and dust that will obscure the visible light from the star. In this stage, it forms a proto-planetary
nebula. Only dim infrared emissions from the dust cloud and reflected starlight let astronomers
see anything at all. Hubble images of this stage show a wide variety
of shapes, hinting at the complex dynamics at work inside. The spiral structure of this nebula is particularly
unusual, and is likely due to a second orbiting star that is producing swirling patterns in
the gas and dust. Over a period of a few thousand years, radiation
from the hot remains of the star excites the gas in the nebula, causing it to glow. The once faint nebula now becomes a bright
and mysterious cloud called a planetary nebula. This type of nebula populates our galaxy…
with luminous shapes that draw the gaze of many a sky watcher. Eventually, planetary nebulae fade to nothing
as their gas and dust diffuse into space. All that remains is the tiny white dwarf — a
form that our Sun will take billions of years from now. Planetary nebulae are more than just beautiful
shapes that grace our galactic skies. They show important stages in the life cycle
of stars… and how they interact with and even shape their surroundings. Hubble has given astronomers the sharpest
views yet of these ghostly, dynamic structures. Take the Ring Nebula, just over 2,000 light
years away from Earth. From Earth’s perspective, it looks like
a simple elliptical body with a fuzzy boundary. But Hubble observations show that the nebula
is shaped more like a distorted doughnut. The doughnut hole may look empty, but it is
full of lower density gas that stretches toward and away from us, creating a shape a little
like a rugby ball that’s been slotted into the doughnut’s hole. The space surrounding the nebula is turbulent
and full of knotty structures that formed long ago. If we were able to rotate the Ring Nebula
by 90 degrees and view it side on, it would look more like the nebula M76, also known
as the “Little Dumbbell.” In the act of dying, sun-like stars cast most
of their mass out into the galactic winds. In time, the atoms in our own sun may well
be swept up into new suns, new solar systems. In the cycles of star birth and star death,
the galaxy is dominated by a rare and extremely violent breed. Stars ten times the mass of our sun, and even
larger, burn hot and fast. Intense temperatures and pressure ignite nuclear
fusion reactions in their cores. Hydrogen gas turns to helium, oxygen, carbon, calcium,
silicon… all the way to iron. The outward pressure from heat radiating from
the star’s core is no longer enough to hold it up under the crushing weight of these elements. Gravity wins the battle… and the star’s
core collapses inward. That produces a shock wave that races out
through the star’s volume and obliterates it. Of the 200 million odd stars in our galaxy,
one goes supernova about every century or so. The last one to be seen in the Milky Way was
observed by the astronomer Johannes Kepler in 1604, just five years before the invention
of the telescope. The most famous supernova in recent years
appeared in 1987 in the Large Magellanic Cloud, a dwarf galaxy just above the plane of the
Milky Way. It was so bright it was visible to the naked
eye. Launched three years later, Hubble has been tracking the evolving spectacle for over
a quarter of a century. Astronomers have marveled at the complexity
of the explosion, including the patterns etched by its expanding shock wave. Even though a supernova is only bright for
a short period of time, the dusty clouds it leaves behind can last for millennia. Their
effect on the surrounding interstellar gas lasts even longer. Although no supernova in our galaxy has ever
been observed with a telescope, plenty of supernova remnants have been. Hubble’s sharp
images of their complex structures help explain the sequence of events… as well as the profound
impact these explosions have on the galaxy. Take the Crab supernova, one of the most interesting,
and most studied, objects in all of astronomy. Japanese and Chinese astronomers witnessed
the explosion in the year 1054. The
filaments shown in these images are the tattered
remains of the star, consisting mostly of hydrogen. The collapsed core of the star embedded
in the center is barely visible in this Hubble image. Yet you can see its effects. The bluish glow
comes from electrons whirling at nearly the speed of light around magnetic field lines
that extend from the star’s collapsed core. Astronomers have been poring over the nebula
itself, still growing at a rate of a thousand kilometers a second. What they’ve found is that the filaments
of matter that roared out of the blast contain large volumes of dust, an array of mostly
carbon or silicate compounds that absorb visible light. These solid particles are crucial for the
formation of solar systems. Within the Crab nebula, there is enough dust to make 30-40,000
Earths. Galaxies all around the universe bear witness
to the dusty legacy of countless supernovae. The bright central region of the famous pinwheel
galaxy, for example, is surrounded by dark, dusty lanes. In spiral galaxies, hot winds from exploding
stars have helped push these clouds toward the periphery as well as above and below their
flat discs. You can see evidence of this in our view of
the Milky Way galaxy. Dark dust lanes and ominous clouds dominate our view into the
disc, while tendrils of dust reach far above it. Some dust clouds are destined to light up
with new stars, as you can see in one of the Milky Way’s small companion galaxies: The
Large Magellanic Cloud. Its most dramatic feature is the Tarantula
Nebula, a bright region of glowing gas and energetic star formation. The Tarantula, shown in a these Hubble images,
glows brightly because hydrogen gas within it is being excited by ultraviolet radiation
from newborn stars. In a wider view, the luminous Tarantula Nebula
stands out from its host galaxy. It is the brightest known star-forming region in the
local Universe and one of the most attractive spots in the night sky. Thanks to Hubble, there is a place within
our own galaxy where you can see not only stars, but solar systems, being born. In the constellation of Orion the Hunter,
just under the three stars that make up its belt, is the majestic Orion Nebula. It draws our attention for its beauty and
mystery. Ancient civilizations saw meaning as well, including the Maya in what is now
southern Mexico and northern Central America. In their story of creation, three of the brightest
stars in the Orion constellation represented a hearth. The nebula was the fire that warms
it. At 1,500 light years distance, it’s one
of the best-known examples of a star-forming nebula – a swirling cloud of gas and dust
where stars begin their journey of life. Within it, Hubble astronomers discovered isolated
pockets of gas called proplyds. These are protoplanetary discs that form around newborn
stars in spinning mixtures of gas and dust. These discs are now thought to be planetary
systems in the making. The brightest star in the Trapezium star cluster
affects the nearby discs by heating up the gas within them, causing them to shine brightly.
The excited material produces many glowing cusps that face the bright star. Other interesting features enhance the look
of these captivating objects, including jets and dramatic shock waves. They are formed
when the stellar wind from the nearby massive star meets gas in the nebula. The interaction produces shapes like boomerangs
or arrows. In one case, the shock wave makes the proplyd look like a space jellyfish. The powerful radiation that allows us to see
these shapes also threatens their existence. Once heated up, the discs are more likely
to dissipate and dissolve, destroying their potential to spawn planets. Some of the bright proplyds are doomed to
be torn apart. The dimmer ones are the most likely to survive. Among those that do produce solar systems,
Hubble has been documenting a wide diversity of planets. One of them, known as HD189733b, is a huge
gas giant similar to Jupiter. It lies extremely close to its star, as shown in this animation. Proximity to the star makes its climate exceptionally
hot, with temperatures exceeding 1000oC. A team of scientists used Hubble to observe
it as it passed in front of its parent star. While backlit in this way, a planet’s atmosphere
imprints its signature on the starlight, allowing astronomers to decode what is happening on
scales far too small to image directly. They expected to confirm that the upper layers
of the planet’s atmosphere are boiling off under the intense starlight. Hubble’s first observations showed no trace
of this. Just before it could take a second look, the
Swift satellite detected a huge flare coming from the surface of the star, with powerful
atmosphere-frying X-rays. When the planet slid into view a few hours
later, the changes were startling. Where astronomers had seen a slumbering planet before, now they
saw an atmosphere furiously boiling away. In a dramatic plume of gas, the planet was
losing at least 1000 tons of gas from its atmosphere every second. There’s no life on a planet that orbits
so close to its parent star. Such planets, however, are allowing Hubble
astronomers to hone their search for Earth-like planets further out. When the planet moves between the star and
Earth, Hubble has been able to capture a small fraction of starlight passing through the
planet’s atmosphere. Astronomers are looking for a hydrogen-carbon
compound called Methane. On Earth, it’s produced by a combination of natural and manmade
sources, including fossil fuel production. On this “hot jupiter,” methane is probably
produced by a complex chemical process in its atmosphere. Astronomers plan to use data to identify prebiotic
molecules in the atmospheres of planets in the “habitable zones” around other stars,
where more moderate temperatures would allow liquid water to flow. The new measurements are an important step
toward the ultimate goal of identifying the conditions, such as temperature, pressure,
winds, clouds, and chemistry on planets where life could exist. Astronomers have detected a wide range of
planets around other stars by looking for clues, like the wobbling motion of a star
as a planet orbits it, or a star getting dimmer as a planet passes in front of it. Hubble was able to capture, for the first
time, a direct image of a planet. Visible from the southern hemisphere, Fomalhaut
is relatively close, at around 25 light-years away. It is 15 times brighter than the sun, and
much hotter. This star is blazing through its hydrogen fuel supply at such a furious
rate that it will burn out in only a billion years, 10% of the lifespan of our star. Its most interesting feature may be a large
disk of dust and gas that surrounds it. This strange ring is not exactly centered
on the star. Astronomers suspect that the gravity of another body — perhaps a planet
— is pulling it out of shape. The suspected planet is a dim speck. To see
it, astronomers used an instrument called a coronagraph to block the star’s light. Then they gathered a host of clues to find
out what it’s like. For one, the shape of the disk hints that
the planet is at most three times the mass of Jupiter. For another, the planet is much brighter than
expected for an object of its size. That means it could have an enormous ring system that
reflects starlight in all directions. One day the material in these rings may even coalesce
to form moons. Hubble is part of a larger quest to discover
and understand solar systems, including our own. Among the highlights, astronomers have used
Hubble to track the changing climate of cloudy Venus. Dust storms that sweep across the planet Mars. The aftermath of comet Shoemaker-Levy’s
collision with Jupiter. Saturn’s stunning rings, and moons. Uranus’ rings. And Neptune’s intense, turbulent atmosphere. In our solar system, few Hubble images compare
to its views of Saturn… And the fluttering aurorae that light up its
poles. Scientists created a movie from data collected
over several days during January and March 2009, when the rings appeared edge-on, and
both poles were visible to us. The Sun emits a wind of particles that reaches
all parts of the Solar System. When this electrically charged stream gets close to a planet with
a magnetic field, like Saturn or the Earth, the field traps these particles. The magnetic field is stronger at the poles,
so the particles tend to concentrate there, where they interact with atoms in the upper
layers of the atmosphere. That’s what creates the familiar nighttime glow we know as the
northern and southern lights. Saturn’s auroras are not only charming features,
but they might teach us something about our own planet and its magnetic field. Beyond Saturn’s dancing lights… or the
sudden explosion of a star… the universe appears unmoving against the ponderous march
of cosmic time. Among its greatest achievements, the Hubble
Space Telescope has been able to track the large-scale motions of the universe. Take an event close to home. Astronomers have
long known that the Andromeda Galaxy, currently 2.5 million light-years away, is moving toward
our Milky Way. A team of astronomers used the Hubble Space
Telescope to find out how fast the two galaxies are moving, and whether there will be head
on collision. They tracked the motion of stars in Andromeda…
then projected their movement into the future. Based on these findings, they showed the course
of events over the next eight billion years, as the galaxies move closer… …then collide… and gradually merge into
a new larger galaxy. If you could wait a few billion years, our
night sky would change dramatically. As Andromeda approaches, it will loom large
in the sky. Later, when the galaxies begin to merge, they
will twist and distort under the pull of their mutual gravity. In time, the new combined galaxy will become
an immense ball of stars… what’s known as an elliptical galaxy. Even though these two galaxies each have hundreds
of billions of stars in them, the stars are all relatively far apart. The chance of any
two colliding is extremely small. Our Sun, born in the Milky Way almost 5 billion
years ago, will follow a new path as it orbits a whole new galaxy. In the universe according to Hubble, galaxies
all around across the cosmos are circling each other… merging… and moving into ever-larger
and denser groupings. Using Hubble to survey patterns of galaxies,
scientists have been able to map a mysterious substance that envelops galaxies and clusters
of galaxies. This so-called “dark matter” adds to the
gravity of these structures and has been driving their collapse over time. Because of the arrangement of galaxies, Astronomers
have long known that dark matter stretches out across the cosmos in a vast web-like structure.
Actually observing this web has been difficult. Now, a team of scientists has used Hubble
to make detailed observations of a dark matter filament, measuring its length, shape and
density. Theories say galaxy clusters form where filaments
of the cosmic web meet. So the team focused Hubble on one such cluster with a stream of
galaxies moving into it along several filaments. The astronomers used data from several ground
telescopes to measure distances to the galaxies within the filament mapped by Hubble, and
to trace their motions. In so doing, they made the first ever three-dimensional
reconstruction of a filament. It extends across at least 60 million light-years
of space. From our perspective, we see it gently curving towards us, then continuing
almost along our line of sight, before it plunges into the back of the galaxy cluster. Observing and reconstructing the cosmic web
can tell us how the universe has evolved to date. Scientists wanted to know how it’s
evolving on an even grander scale. If dark matter dominates the cosmos, will
its gravity be enough to cause the universe itself to crash together in a heap at some
point in the distant future? To find out, they searched for a type of exploding
star that’s visible across the cosmos. It is the product of a small burned out star
called a white dwarf that orbits a larger star. The smaller star pulls matter from its neighbor,
thereby gradually increasing its mass. Finally, when it reaches a critical mass,
it undergoes a thermonuclear explosion. These so-called Type 1A explosions are thought
to all have the same intrinsic brightness. How bright they appear to us is a measure
of how far away they are. What the scientists found is that the most
distant of the explosions were much fainter than they expected. They deduced from this
data that the space between Earth and those distant explosions had been expanding faster
and faster. Scientists theorized that another unknown
force, dark energy, is actually pushing the universe apart at an accelerating rate. This means that the universe will not collapse
in a heap. Rather, it will keep on expanding forever…. Until all matter and energy eventually
dissipate to nothingness. In our time, the light of the universe continues
to rain down on Earth in torrents, a measure of the energy emitted in a constant process
of creation and destruction. Hubble has led a broad effort to capture this
light in telescopes stationed both on mountaintops and in space. Through their lenses, we have seen a universe
that is evolving on all time scales, from the very short to the very long. In its own brief time in space, Hubble has
revolutionized the science of astronomy… while inspiring untold legions of stargazers.