Our
galaxy, the Milky Way, contains a supermassive black hole at its core
surrounded by a central bulge of old, yellowish stars. Beyond that are
bluish spiral arms filled with younger stars, newly forming stars, and
dark lanes of dust.
It is just one of billions of
galaxies in our universe, but the Milky Way is our galaxy, our home in
the universe. The Milky Way contains the closest examples of stars,
planets, nebulae, black holes, and other objects that likely reside in
every galaxy throughout the cosmos. By studying the Milky Way in the
infrared, the Webb Telescope will be able to teach us a great deal about
our galaxy and others.
Webb will improve our understanding of all stages of star formation —
from birth to death and back again to the rise of the next stellar
generation. Astronomers know that stars form out of collapsing clouds of
gas and dust, but they don't yet know the exact sequence of how stars
are born. What triggers a cloud to collapse and a star to begin forming?
How much of that mother cloud does a star use up when it forms? How and
when do planets begin to form around a newborn star?
At the end of their lives, stars die in a variety of exciting and
interesting ways — from gentle exhales of material to violent explosions
expelling stellar shrapnel into the galaxy. Many dying stars and
stellar corpses are embedded in their ejected material, which shrouds
our view in visible light but can be penetrated with Webb's infrared
vision. Webb will help us probe and understand both this residual
material and the stars that died. It will help astronomers test their
theories for how stars end their lives and how the heavier elements
forged within these dying stars are recycled into the galactic
environment to help create the next generation of stars.
Omega Centuari is one of the largest globular star clusters residing in the outskirts of our galaxy.
Counting Stars
Webb will help us understand just how many stars there are and how
those stars are distributed throughout the galaxy. The most common stars
in the Milky Way are "dwarf" stars that are often too dim for Hubble to
observe in visible light, but that glow brighter in infrared light.
Webb will help astronomers get a firmer grip on just how many of these
stars exist, and perhaps help us learn more about them. Knowing how many
stars there are of different types also tells us how quickly or
efficiently stars formed at various stages in the galaxy's history.
Webb will also study giant stellar swarms called globular clusters,
which reside at the outskirts of the Milky Way and contain the oldest
stars in the galaxy. Webb will analyze the composition of these ancient
stars, and perhaps reveal whether globular clusters formed along with
our galaxy or originated somewhere else, and were later absorbed into
the galaxy.
Looking Inward and Outward
This
X-ray image shows the region around our galaxy's central supermassive
black hole, known as Sagittarius A* (or Sgr A*). Credit: NASA/CXC/Univ.
of Wisconsin/Y. Bai et al.
Webb will help us
understand what's going on at the very heart of the Milky Way. In our
galaxy's core lies a supermassive black hole surrounded by gas, dust,
and a densely packed swarm of stars. However, this central black hole
does not seem to be consuming as much material as its peers in other
galaxies are. Astronomers aren't sure why. Webb’s infrared observations
could give us a clearer view of the material and stars near the black
hole, and perhaps uncover the reason why our galaxy's black hole is so
quiet.
Webb's sharp and powerful infrared vision will allow it to peer
farther into the Milky Way with greater clarity than infrared telescopes
before it — uncovering parts of the galaxy that were once too dim, too
distant, or too concealed to study. These investigations will not only
help us understand our own Milky Way, but myriad galaxies throughout the
universe.
Hubble's infrared vision reveled more than half a million stars at the core of the Milky Way.
Our
solar system resides in one of the spurs off the spiral arms of the
Milky Way galaxy, and we tend to think of our experience of the Milky
Way as typical. Even in our science fiction films, when the heroes
travel between stars, every sky looks the same.
But the Milky Way isn't quite so uniform. If you lived in the center
of the Milky Way, you could look up on a sky thick with stars, a
thousand to a million times more than we're used to seeing, depending on
how close you were to the core. For Earth's inhabitants, the next
closest star to our Sun is about 4 light-years away. For our central
Milky Way cousins, that star would be around 0.4–0.04 light-years
distant.
The center of the Milky Way consists of the region where the galaxy's
spiral arm structure has broken down and transformed into a "bulge" of
stars, or roughly the inner 10,000 light-years. At its heart — and the
dominant force in that area of the galaxy — is a million-solar-mass
black hole we call Sagittarius A*.
It would be an inhospitable area for humanity, rife with radiation
emanating from a surplus of massive stars and material being torn apart
by the black hole. Plus it would take us more than 25,000 years to reach
it, even if we could travel close to the speed of light. Fortunately,
the Webb telescope is designed to do our exploring of the galactic
center for us.
This
simulated image shows a supermassive black hole at the core of a
galaxy. The black region in the center represents the event horizon,
where no light can escape the massive object's gravitational pull. The
black hole's powerful gravity distorts the space around it, stretching
light from background stars.
Sleeping Giant
Our central, supermassive black hole is relatively quiet when
compared to its counterparts in other galaxies, flaring only
occasionally with X-rays and infrared light as objects fall into it. It
could be that there's simply not that much material around Sagittarius
A*. Webb will investigate our strangely calm central black hole,
providing a more accurate measurement of its mass, as well as how much
material is falling into it, and when. Furthermore, the mass of our
black hole ranges on the low end of normal for galaxies of our size.
Webb will examine why that is and the relationship between a black hole
and the matter surrounding it.
While Webb helps reveal why we have the kind of black hole that we
do, it'll also be shedding light on central, supermassive black holes in
other galaxies. Active galactic nuclei (AGN) are a type of extremely
bright galaxy core seemingly fueled by powerful black holes actively
gobbling large amounts of material. Astronomers would like to know what,
exactly, AGN are and if they are triggered by events occurring in the
centers of galaxies or by mergers between galaxies.
Webb's investigations of our own black hole and the relationship
between black holes and galaxy evolution could help solve a cosmic
chicken-and-egg problem: Did black holes come first and galaxies form
around them, did galaxies form first and develop black holes, or did the
galaxies and black holes develop together?
Hubble
captured the Eagle Nebula in visible light (left) and infrared light
(right) in 2015. While the visible-light image shows opaque clouds,
infrared light penetrates gas and dust, revealing both stars behind the
nebula and those hidden away inside the pillar.
Stars
form from collapsing clouds of gas and dust. It's a process that
occurred in our distant past and continues to take place today.
Astronomers can train their telescopes on giant clouds of hydrogen gas
in our own galaxy and find knots of denser, colder gas and dust that are
in the process of giving rise to stars.
But these dust-thick regions of starbirth are often dark and opaque.
The Pillars of Creation in the Eagle Nebula, depicted in one of Hubble's
most famous images, is a stellar nursery, but what we see of it looks
like a dense cloud.
In 2015, Hubble revisited the Eagle Nebula to create two new images
of that famous region — one capturing visible light, and the other
near-infrared.
This
young cluster of about 3,000 stars in our Milky Way is called
Westerlund 2 and contains some of the galaxy's hottest, brightest, and
most massive stars. Hubble's infrared vision pierced dust around this
stellar nursery to reveal the dense concentration of stars in the
central cluster.
The pictures illustrate the
striking difference between what visible-light telescopes like Hubble
see, and what infrared telescopes like Webb will show us. In the
near-infrared image, the clouds are transformed into ghostly outlines
and hidden stars blaze forth from both within and beyond. Newborn stars
shine dramatically from within the cloud.
Infrared light, unlike visible light, travels through dust clouds.
And cameras that can capture it can see through such clouds as though
they were nearly invisible. Furthermore, Webb's cameras will detect the
infrared glow of the dust and gas itself, allowing us to learn what it's
made of, how hot and dense it is, and what chemical processes have
affected it. These abilities will make Webb a critical tool for learning
just how star formation works within those dusty depths.
Seeing Stars
For instance, astronomers know collapsing clouds have a point of no
return, when they become so dense and so cold that they cannot hold
themselves together against collapse. Above this threshold stars form,
below it they don't. But the gas drifting between stars isn't dense
enough by itself to trigger star formation. Is star formation triggered
mainly by shockwaves from exploding stars, or the pressure created by
radiation and stellar winds from massive stars — or can those processes
get in the way of the collapse? Could star formation begin with the
collision and accumulation of sparse pockets of dust and gas? Do stars
compete for material in the cloud, or do they form mostly in isolation?
Does the entire cloud collapse into stars at the same time, or do stars
form in groups? With its powerful infrared sensitivity and resolution,
Webb will be able to peer into star-forming regions across the entire
Milky Way galaxy, where previous infrared telescopes were limited to
dust clouds within our own galactic neighborhood. Webb will collect a
wide array of examples to give astronomers plenty of star-formation
regions to compare.
Twinkle, twinkle, little star How I wonder what you are
It’s not easy to tell a star from a planet when you look up at the
night sky. Ancient astronomers noted that some lights moved across the
sky, while others appeared to remain in a fixed position. The Greeks,
picking up the work of these earlier scientists, called such a
travelling point of light planēs – wanderer. We still call them planets today.
But other than orbiting around a star, what makes a planet a planet? As telescopes become more sophisticated
and we learn more about the universe, the less some old definitions
make sense. We now know that some planets are rocky, like Earth, while
others are so-called gas giants, like Jupiter.
We also know that our middle-aged Sun is one type of a variety of
stars, classified by their phase in a lifecycle we are still in the
process of understanding. A star shines by producing its own light from
nuclear fusion in its dense, hot core. Planets shine—to our eyes on
Earth—by reflecting the light of stars.
These were the simple, sharp definitions of stars and planets until
the discovery of a brown dwarf in 1995. Theorized as early as the 1960s,
this new type of celestial body blurred the line between star and
planet, requiring an exciting re-thinking of the universe.
An
artist’s depiction of the relative sizes of the Sun, a low mass star, a
brown dwarf, Jupiter, and the Earth. Credit: NASA/JPL-Caltech/UCB
Despite their name, brown dwarfs can be up to 70 times more massive
than gas giants like Jupiter. Brown dwarfs form like stars do, by the
contraction of gas that collapses into a dense core under the force of
its own gravity, whereas planets form from the accumulation of leftover
debris from these stellar births. However, brown dwarfs do not have
enough mass for their cores to burn nuclear fuel and radiate starlight.
This is why they are sometimes referred to as “failed stars.” They are
smaller and cooler than the Sun, and have complex planet-like outer
atmospheres, including clouds and molecules such as H2O.
Astronomers now disagree on whether some “free-floating” bodies detected
in space – not orbiting a star, but also not shining like a star –
should be called planets or brown dwarfs.
A brown dwarf atmosphere is easier to study than that of an
exoplanet, which is typically obscured in the blinding light of its
parent star. But to study brown dwarfs you first have to find them.
Their dim light makes this difficult, and eventually the visible light
left over from their birth fades completely beyond the red end of the
visible spectrum, and they emit only infrared light.
Credit: STScI
Difficult to detect, brown dwarfs hint at the many undiscovered wonders
the universe still holds, hidden for centuries beyond the bounds of
visible light. Much of the mass that holds the universe together with
its gravity has thus far been undetectable, and is known as dark matter.
In 2019, the James Webb Space Telescope will continue the work of
NASA’s Hubble Space Telescope and infrared Spitzer Space Telescope in
probing the furthest and “darkest” regions of the universe. Webb will
see farther and in higher resolution, with unprecedentedly powerful
infrared cameras and spectrographs. When Hubble launched, the only
planets we knew of were those in our own Solar System. There were no
images of brown dwarfs. Webb will take a detailed look at the
atmospheres of brown dwarfs and exoplanets, determining their
temperatures and chemical compositions.
Do the traditional boundaries between planets and stars still make
sense? Once purely philosophical, these questions now loom large in
science. With infrared observations, the Webb Telescope will add to our
understanding of the universe’s ongoing evolution, and the place of
Earth and our Solar System within that bigger picture.
Elon Musk just unveiled more of his grand plan for colonizing Mars.
The hard-charging tech mogul said his rocket company, SpaceX,
aims to land at least two cargo ships on the Red Planet in 2022 in
order to place power, mining and life support systems there for future
flights.
That's just five years from now.
"That's not a typo -- although it is aspirational," Musk said Friday
during a presentation at the International Astronautical Congress in
Australia. Ships carrying crews would arrive in 2024, he added.
To hit those deadlines, SpaceX plans to start building the first
spaceship by the middle of next year, he said. The billionaire
entrepreneur does have a track record of setting ambitious time frames for SpaceX, and failing to meet them.
Musk revealed more details on the spacecraft -- the BFR, or Big Falcon
Rocket, which inside the company is nicknamed the "Big F--king Rocket."
If he has his way, Mars colonizers will eventually travel in style in
the BFR, which will accommodate around 100 people spread out over 40
cabins, and include large common areas and an entertainment system.
SpaceX has figured out a way to pay for the costly missions,
according to Musk, but he shied away from giving specific numbers.
The company thinks it can make enough money from its current business
of launching satellites and servicing the International Space Station to
finance its Mars ambitions. Musk's goal is to make the BFR reusable,
which would significantly bring down the cost of launches.
He envisions the rockets enabling SpaceX to eventually establish a lunar base, which he dubbed "Moon Base Alpha."
"It's 2017, we should have a lunar base by now," he said. "What the hell's going on?"
Musk suggested the BFR could eventually also be used to clean up
space by gobbling up old satellites and other junk orbiting the earth.
And it may come in handy closer to home. Musk said the rockets could fly people from city to city on Earth in incredibly short time spans, such as from New York to Shanghai in 39 minutes. Related: Elon Musk wants to fly you anywhere in the world in less than an hour
SpaceX isn't the only company with an eye on Mars, though.
Just hours before Musk took the stage in Australian city of Adelaide on Friday, Lockheed Martin (LMT) touted its plans for a "Mars Base Camp" -- a mobile space habitat that
it's developing for NASA. The system would work in tandem with Orion,
the spacecraft NASA is developing for crewed missions to deep space.
Lockheed said the structure could be assembled at NASA's Deep Space
Gateway -- a structure the agency is developing that would live in space
between Earth and the Moon. Related: Branson! Musk! Bezos! The billionaire space race throwdown
The company says it hopes to build and send the structure to the Mars in about 10 years.
Unlike SpaceX's plan, NASA and Lockheed aren't looking to colonize
Mars. Their project is focused on executing experimental missions in
which highly trained astronauts would visit the planet and ultimately
return to Earth.
Aerospace giant Boeing (BA) has also said it wants the first person to set foot on Mars to get there on one of its rockets.
The Cassini spacecraft spent just over 13 years in the Saturn system,
studying this massive, gaseous planet, its rings and its moons. Thanks
to gravity assists from Saturn's moon Titan, the probe was able to
change its orbit around the planet many times, and view the planet from
various angles. In total, the probe sent back more than 450,000 images
of the Saturn system. That's a lot to sift through, but we think these
are some of the most spectacular images Cassini took of Saturn.
1. End of an era
Saturn's
largest moon, Titan, can be seen beyond the rings 2. Rings and Waves
Cassini
captured this view of a wave structure in Saturn's rings, known as the Janus
2:1 spiral density wave. Resulting from the same process that creates spiral
galaxies, spiral density waves in Saturn's rings are much more tightly wound
3. Ring Shadows
The
shadow of Saturn's rings appear as a thin band at the equator in this image
that was taken by Cassini as Saturn approached its August 2009 equinox.
4. Planetary portrait
Credit:
NASA/JPL/Space Science Institute
Cassini snapped this photo as it
rested in Saturn's shadow, producing a stunning image where the planet's inner
rings, seven of its moons and Earth can be seen.
5. Rainbow on the rings
Cassini's spacecraft offered
unprecedented views of Saturn and its moons, including this photo of a rainbow
on the planet's rings.
6. Colorful pole
This spectacular, vertigo-inducing,
false-color image from NASA Cassini mission highlights the storms at Saturn's
north pole. The angry eye of a hurricane-like storm appears dark red.
7. Unique image
In a rare wide-angle camera image
from Cassini, Saturn's rings and Earth (seen here as a bright speck) share
space.
8. Titan's
seas
This
near-infrared, color view shows the sun glinting off of Titan's north polar
seas.
9.Venus
through the Rings
Peering over the shoulder of Saturn, through its
rings, and across interplanetary space, the Cassini spacecraft spies the
bright, cloudy planet Venus
10. Trio
of moons
Cassini observes three of Saturn's
moons set against the darkened night side of the planet. Seen here are Rhea,
closest to Cassini, Enceladus to right of Rhea, and Dione, to the left of Rhea.
11. Geysers
on Enceladus
This image from Cassini, one that
was acquired in a survey conducted by the spacecraft's imaging science team,
shows the geyser basin at the south pole of Enceladus.
12. Light
and shadow
Capturing the interplay between
light and shadow, NASA's Cassini spacecraft looks toward the night side of
Saturn, where sunlight reflected off the rings has dimly illuminated what would
otherwise be the dark side of the planet.
13. Dione
Saturn's pale, icy moon Dione is
enriched by the tranquil gold and blue hues of Saturn in the distance. The
horizontal stripes near the bottom of the image are Saturn's rings.
14. Farewell,
Mimas
On Jan. 30, 2017, Cassini bid so
long to Saturn's "Death Star"-like moon Mimas.
15. Mind
the gap
Saturn's moon Pan is seen in this
color view as it sweeps through the so-called Encke Gap in Saturn's rings. As
the lemon-shaped moon orbits Saturn, it always keeps its long axis pointed
along a line toward the planet
16. Shadowy
moon
Jagged-looking shadows stretch away
from vertical structures of ring material created by the moon Daphnis in this
image taken as Saturn approached its August 2009 equinox.
17. Titan
and Mimas
Cassini captures a mutual event
between Titan and Mimas in front of a backdrop of Saturn's rings. This image
was snapped shortly before Saturn's largest moon passed in front of and
occulted the small moon Mimas.
18. Dione's
closeup
This view of Saturn's moon Dione was
taken during a close flyby on June 16, 2015. It was Cassini's fourth targeted
flyby of Dione.
19. Moon's
gravity
The gravity of the potato-shaped
Prometheus periodically creates streamer channels in Saturn's rings. The moon's
handiwork can be seen in the dark channels in this image taken by the Cassini
spacecraft.
.
20. Dione
in transit
Saturn's moon Dione crosses the face
of the giant planet in this view, a phenomenon astronomers call a transit.
21. Icy
Enceladus
On Oct. 14, 2015, the Cassini spacecraft snapped
a ethereal image of Enceladus' icy north pole
22. Ligeia
Mare
This image, from the Radar
instrument aboard the Cassini spacecraft, shows the evolution of a transient
feature in the large hydrocarbon sea named Ligeia Mare on Saturn's moon Titan.
23. Herschel
Crater
Shadows cast across Mimas' defining
feature, Herschel Crater, provide an indication of the size of the crater's
towering walls and central peak.
24. Polar
Hexagon
These natural color views compare
the appearance of Saturn's north-polar region in June 2013 and April 2017. In
both views, Saturn's polar hexagon dominates the scene.
Before NASA's Cassini spacecraft began the "grand finale" phase of its
mission at Saturn, it took one last photo of the giant planet and its
ring system from afar
ff
Cassini's Last Photo
Credit: NASA/JPL-Caltech/Space Science Institute
This is the last
image taken by NASA's Cassini spacecraft before it dove into Saturn's
atmosphere. It shows the location where the spacecraft would enter the
planet's atmosphere hours later. Cassini took the photo on Sept. 14,
2017 at 12:59 p.m. PDT (3:59 p.m. EDT; 19:59 GMT).
Saturn
Credit: NASA/JPL-Caltech/Space Science Institute
Cassini shot this photo of Saturn on Sept. 13, 2017.
