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Hubble in pictures: astronomers' top picks
Astronomers from around the world identify their favourite images sent back to Earth by the Hubble Space Telescope.
In
this special feature, we have invited top astronomers to handpick the
Hubble Space Telescope image that has the most scientific relevance to
them. The images they’ve chosen aren’t always the colourful glory shots
that populate the countless “best of” galleries around the internet, but
rather their impact comes in the scientific insights they reveal.
Tanya Hill, Museum Victoria
NASA,ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team
My all-time favourite astronomical object is the
Orion Nebula –
a beautiful and nearby cloud of gas that is actively forming stars. I
was a high school student when I first saw the nebula through a small
telescope and it gave me such a sense of achievement to manually point
the telescope in the right direction and, after a fair bit of hunting,
to finally track it down in the sky (there was no automatic ‘go-to’
button on that telescope).
Of course, what I saw on that long ago
night was an amazingly delicate and wispy cloud of gas in black and
white. One of the wonderful things that Hubble does is to reveal the
colours of the universe.
And this image of the Orion Nebula, is our best chance to imagine what
it would look like if we could possibly go there and see it up-close.
So
many of Hubble’s images have become iconic, and for me the joy is
seeing its beautiful images bring science and art together in a way that
engages the public. The entrance to my office, features an enormous
copy of this image wallpapered on a wall 4m wide and 2.5m tall. I can
tell you, it’s a lovely way to start each working day.
Michael Brown, Monash University
The impact of the fragments of
Comet Shoemaker Levy 9 with
Jupiter in July 1994 was the first time astronomers had advance warning
of a planetary collision. Many of the world’s telescopes, including
the
recently repaired Hubble, turned their gaze onto the giant planet.
The comet crash was also my first professional experience of observational astronomy. From a frigid
dome on
Mount Stromlo,
we hoped to see Jupiter’s moons reflect light from comet fragments
crashing into the far side of Jupiter. Unfortunately we saw no flashes
of light from Jupiter’s moons.
However, Hubble got an amazing and unexpected view. The impacts on the far side of Jupiter produced
plumes that rose so far above Jupiter’s clouds that they briefly came into view from Earth.
As
Jupiter rotated on its axis, enormous dark scars came into view. Each
scar was the result of the impact of a comet fragment, and some of the
scars were larger in diameter than our moon. For astronomers around the
globe, it was a jaw dropping sight.
William Kurth, University of Iowa
NASA, ESA and Jonathan Nichols (University of Leicester), CC BY
This
pair of images shows a spectacular ultraviolet aurora light show
occurring near Saturn’s north pole in 2013. The two images were taken
just 18 hours apart, but show changes in the brightness and shape of the
auroras. We used these images to better understand how much of an
impact the
solar wind has on the auroras.
We used Hubble photographs like these acquired by my astronomer colleagues to monitor the auroras while using the
Cassini spacecraft, in orbit around Saturn, to observe
radio emissions associated with the lights. We were able to determine that the brightness of the auroras is correlated with higher radio intensities.
Therefore,
I can use Cassini’s continuous radio observations to tell me whether or
not the auroras are active, even if we don’t always have images to look
at. This was a large effort including many Cassini investigators and
Earth-based astronomers.
John Clarke, Boston University
NASA and John Clarke (Boston University), CC BY
This
far-ultraviolet image of Jupiter’s northern aurora shows the steady
improvement in capability of Hubble’s scientific instruments. The Space
Telescope Imaging Spectrograph (
STIS) images showed, for the first time, the full range of auroral emissions that we were just beginning to understand.
The earlier Wide Field Planetary Camera 2 (
WFPC2)
camera had shown that Jupiter’s auroral emissions rotated with the
planet, rather than being fixed with the direction to the sun, thus
Jupiter did not behave like the Earth.
We knew that there were aurora from the mega-ampere
currents flowing from Io along
the magnetic field down to Jupiter, but we were not certain this would
occur with the other satellites. While there were many ultraviolet
images of Jupiter taken with STIS, I like this one because it clearly
shows the auroral emissions from the magnetic footprints of Jupiter’s
moons Io, Europa, and Ganymede, and Io’s emission clearly shows the
height of the auroral curtain. To me it looks three-dimensional.
Fred Watson, Australian Astronomical Observatory
Take a good look at these images of the
dwarf planet,
Pluto, which show detail at the extreme limit of Hubble’s capabilities.
A few days from now, they will be old hat, and no-one will bother
looking at them again.
Why? Because in early May, the
New Horizons spacecraft will be close enough to Pluto for its cameras to reveal better detail, as the craft nears its 14 July rendezvous.
Yet
this sequence of images – dating from the early 2000s – has given
planetary scientists their best insights to date, the variegated colours
revealing subtle variations in Pluto’s surface chemistry. That
yellowish region prominent in the centre image, for example, has an
excess of frozen carbon monoxide. Why that should be is unknown.
The
Hubble images are all the more remarkable given that Pluto is only 2/3
the diameter of our own moon, but nearly 13,000 times farther away.
Chris Tinney, University of New South Wales
HST / Adam Schneider (University of Toledo)/Chris Tinney (UNSW)
I once dragged my wife into my office to proudly show her the results of some imaging observations made at the
Anglo-Australian Telescope with
a (then) new and (then) state-of-the-art 8,192 x 8,192 pixel imager.
The images were so large, they had to be printed out on multiple A4
pages, and then stuck together to create a huge black-and-white map of a
cluster of galaxies that covered a whole wall.
I was crushed when she took one look and said: “Looks like mould”.
Which just goes to show the best science is not always the prettiest.
My
choice of the greatest image from HST is another black-and-white image
from 2012 that also “looks like mould”. But buried in the heart of the
image is an apparently unremarkable faint dot. However it represents the
confirmed detection of the coldest example of a
brown dwarf then discovered. An object lurking less than 10
parsecs (32.6 light years) away from the sun with a temperature of about 350 Kelvin (77 degrees Celsius) – colder than a cup of tea!
And to this day it remains one of the coldest compact objects we’ve detected outside out solar system.
Lucas Macri, Texas A&M University
NASA/ESA/STScI,
processing by Lucas Macri (Texas A&M University). Observations
carried out as part of HST Guest Observer program 9810.
In 2004, I was part of a team that used the recently-installed Advanced Camera for Surveys (
ACS) on Hubble to observe a small region of the disk of a nearby spiral galaxy (
Messier 106) on 12 separate occasions within 45 days. These observations allowed us to discover over
200 Cepheid variables,
which are very useful to measure distances to galaxies and ultimately
determine the expansion rate of the universe (appropriately named the
Hubble constant).
This
method requires a proper calibration of Cepheid luminosities, which can
be done in Messier 106 thanks to a very precise and accurate
estimate of the distance to
this galaxy (24.8 million light-years, give or take 3%) obtained via
radio observations of water clouds orbiting the massive black hole at
its center (not included in the image).
A few years later, I was
involved in another project that used these observations as the first
step in a robust cosmic distance ladder and determined the
value of the Hubble constant with a total uncertainty of 3%.
Howard Bond, Pennsylvania State University
One
of the images that excited me most – even though it never became famous
– was our first one of the light echo around the strange explosive
star
V838 Monocerotis.
Its eruption was discovered in January 2002, and its light echo was
discovered about a month later, both from small ground-based telescopes.
Although
light from the explosion travels straight to the Earth, it also goes
out to the side, reflects off nearby dust, and arrives at Earth later,
producing the “echo.”
Astronauts had serviced Hubble in
March 2002, installing the new Advanced Camera for Surveys (
ACS). In April, we were one of the first to use ACS for science observations.
I
always liked to think that NASA somehow knew that the light from V838
was on its way to us from 20,000 light-years away, and got ACS installed
just in time! The image, even in only one color, was amazing. We
obtained
many more Hubble observations of the echo over
the ensuing decade, and they are some of the most spectacular of all,
and VERY famous, but I still remember being awed when I saw this first
one.
Philip Kaaret, University of Iowa
Galaxies
form stars. Some of those stars end their “normal” lives by collapsing
into black holes, but then begin new lives as powerful X-ray emitters
powered by
gas sucked off a companion star.
I
obtained this Hubble image (in red) of the Medusa galaxy to better
understand the relation between black hole X-ray binaries and star
formation. The striking appearance of the Medusa arises because it’s a
collision between two galaxies – the “hair” is remnants of one galaxy
torn apart by the gravity of the other. The blue in the image shows
X-rays, imaged with the
Chandra X-ray Observatory. The blue dots are black hole binaries.
Earlier
work had suggested that the number of X-ray binaries is simply
proportional to the rate at which the host galaxy forms stars. These
images of the Medusa allowed us to show that the same relation holds,
even in the midst of galactic collisions.
Mike Eracleous, Pennsylvania State University
Some
of the Hubble Space Telescope images that appeal to me a great deal
show interacting and merging galaxies, such as the Antennae (
NGC 4038 and NGC 4039), the Mice (
NGC 4676), the Cartwheel galaxy (
ESO 350-40), and many others without nicknames.
These
are spectacular examples of violent events that are common in the
evolution of galaxies. The images provide us with exquisite detail about
what goes on during these interactions: the distortion of the galaxies,
the channeling of gas towards their centers, and the formation of
stars.
I find these images very useful when I explain to the general public the context of my own research, the
accretion of gas by the supermassive black holes at the centers of such galaxies. Particularly neat and useful is a
video put together by Frank Summers at the Space Telescope Science Institute (
STScI), illustrating what we learn by comparing such images with models of galaxy collisions.
Michael Drinkwater, University of Queensland
NASA, Holland Ford (JHU), the ACS Science Team and ESA
Our
best computer simulations tell us galaxies grow by colliding and
merging with each other. Similarly our theories tell us that when two
spiral galaxies collide, they should form a large elliptical galaxy. But
actually seeing it happen is another story entirely!
This
beautiful Hubble image has captured a galaxy collision in action. This
doesn’t just tell us that our predictions are good, but it lets us start
working out the details because we can now see what actually happens.
There
are fireworks of new star formation triggered as the gas clouds collide
and huge distortions going on as the spiral arms break up. We have a
long way to go before we’ll completely understand how big galaxies form,
but images like this are pointing the way.
Roberto Soria, ICRAR-Curtin University
NASA and The Hubble Heritage Team (STScI/AURA)
This is the highest-resolution view of a collimated jet powered by a supermassive black hole in the nucleus of the
galaxy M87(the biggest galaxy in the
Virgo Cluster, 55 million light years from us).
The
jet shoots out of the hot plasma region surrounding the black hole (top
left) and we can see it streaming down across the galaxy, over a
distance of 6,000 light-years. The white/purple light of the jet in this
stunning image is produced by the stream of electrons spiralling around
magnetic field lines at a speed of approximately 98% of the speed of
light.
Understanding the energy budget of black holes is a
challenging and fascinating problem in astrophysics. When gas falls into
a black hole, a huge amount of energy is released in the form of
visible light, X-rays and jets of electrons and positrons travelling
almost at the speed of light. With Hubble, we can measure the size of
the black hole (a thousand times bigger than the
central black hole of our galaxy), the energy and speed of its jet, and the structure of the magnetic field that collimates it.
Jane Charlton, Pennsylvania State University
When
my Hubble Space Telescope proposal was accepted in 1998 it was one of
the biggest thrills of my life. To imagine that, for me, the telescope
would capture
Stephan’s Quintet, a stunning compact group of galaxies!
Over
the next billion years Stephan’s Quintet galaxies will continue in
their majestic dance, guided by each other’s gravitational attraction.
Eventually they will merge, change their forms, and ultimately become
one.
We have since observed several other compact groups of
galaxies with Hubble, but Stephan’s Quintet will always be special
because its gas has been released from its galaxies and lights up in
dramatic bursts of intergalactic star formation. What a fine thing to be
alive at a time when we can build the Hubble and push our minds to
glimpse the meaning of these signals from our universe. Thanks to all
the heroes who made and maintained Hubble.
Geraint Lewis, University of Sydney
NASA, Andrew Fruchter and the ERO Team [Sylvia Baggett (STScI), Richard Hook (ST-ECF), Zoltan Levay (STScI)] (STScI)
When Hubble was launched in 1990, I was beginning my PhD studies into
gravitational lensing, the action of mass bending the paths of light rays as they travel across the universe.
Hubble’s image of the massive galaxy cluster,
Abell 2218, brings this gravitational lensing into sharp focus, revealing how the massive quantity of
dark matter present
in the cluster – matter that binds the many hundreds of galaxies
together – magnifies the light from sources many times more distant.
As
you stare deeply into the image, these highly magnified images are
apparent as long thin streaks, the distorted views of baby galaxies that
would normally be impossible to detect.
It gives you pause to
think that such gravitational lenses, acting as natural telescopes, use
the gravitational pull from invisible matter to reveal amazing detail of
the universe we cannot normally see!
Rachel Webster, University of Melbourne
Gravitational
lensing is an extraordinary manifestation of the effect of mass on the
shape of space-time in our universe. Essentially, where there is mass
the space is curved, and so objects viewed in the distance, beyond these
mass structures, have their images distorted.
It’s somewhat like
a mirage; indeed this is the term the French use for this effect. In
the early days of the Hubble Space Telescope, an image appeared of the
lensing effects of a massive cluster of galaxies: the tiny background
galaxies were stretched and distorted but embraced the cluster, almost
like a pair of hands.
I was stunned. This was a tribute to the
extraordinary resolution of the telescope, operating far above the
Earth’s atmosphere. Viewed from the ground, these extraordinary thin
wisps of galactic light would have been smeared out and not
distinguishable from the background noise.
My third year astrophysics class explored the
100 Top Shots of Hubble,
and they were most impressed by the extraordinary, but true colours of
the clouds of gas. However I cannot go past an image displaying the
effect of mass on the very fabric of our universe.
Kim-Vy Tran, Texas A&M
With
General Relativity, Einstein postulated that matter changes space-time
and can bend light. A fascinating consequence is that very massive
objects in the universe will magnify light from distant galaxies, in
essence becoming cosmic telescopes.
With the Hubble Space
Telescope, we have now harnessed this powerful ability to peer back in
time to search for the first galaxies.
This Hubble image shows a
hive of galaxies that have enough mass to bend light from very distant
galaxies into bright arcs. My first project as a graduate student was to
study these remarkable objects, and I still use the Hubble today to
explore the nature of galaxies across cosmic time.
Alan Duffy, Swinburne University of Technology
NASA, ESA, H. Teplitz, M. Rafelski (IPAC/Caltech), A. Koekemoer
(STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)
To
the human eye, the night sky in this image is completely empty. A tiny
region no thicker than a grain of rice held at arms length. The Hubble
Space Telescope was pointed at this region for 12 full days, letting
light hit the detectors and slowly, one by one, the galaxies appeared,
until the entire image was filled with 10,000 galaxies stretching all
the way across the universe.
The most distant are tiny red dots
tens of billions of light years away, dating back to a time just a few
hundred million years after the Big Bang. The scientific value of this
single image is enormous. It revolutionised our theories both of how
early galaxies could form and how rapidly they could grow. The history
of our universe, as well as the rich variety of galaxy shapes and sizes,
is contained in a single image.
To me, what truly makes this
picture extraordinary is that it gives a glimpse into the scale of our
visible universe. So many galaxies in so small an area implies that
there are 100 thousand million galaxies across the entire night sky. One
entire galaxy for every star in our Milky Way!
James Bullock, University of California, Irvine
This is what Hubble
is all about.
A single, awe-inspiring view can unmask so much about our Universe: its
distant past, its ongoing assembly, and even the fundamental physical
laws that tie it all together.
We’re peering through the heart of
a swarming cluster of galaxies. Those glowing white balls are giant
galaxies that dominated the cluster center. Look closely and you’ll see
diffuse shreds of white light being ripped off of them! The cluster is
acting like a gravitational blender, churning many individual galaxies
into a single cloud of stars.
But the cluster itself is just the
first chapter in the cosmic story being revealed here. See those faint
blue rings and arcs? Those are the distorted images of other galaxies
that sit far in the distance.
The immense gravity of the cluster
causes the space-time around it to warp. As light from distant galaxies
passes by, it’s forced to bend into weird shapes, like a
warped magnifying glass would distort and brighten our view of a faint candle. Leveraging our understanding of Einstein’s
General Relativity,
Hubble is using the cluster as a gravitational telescope, allowing us
to see farther and fainter than ever before possible. We are looking far
back in time to see galaxies as they were more than 13 billion years
ago!
As a theorist, I want to understand the full life cycle of
galaxies – how they are born (small, blue, bursting with new stars), how
they grow, and eventually how they die (big, red, fading with the light
of ancient stars). Hubble allows us to connect these stages. Some of
the faintest, most distant galaxies in this image are destined to become
monster galaxies like those glowing white in the foreground. We’re
seeing the distant past and the present in a single glorious picture.
This article was originally published on The Conversation.