Artist's conception of the Milky Way galaxy. Credit: Nick Risinger
When you look up at the night sky, assuming conditions are just right, you might just catch a glimpse of a faint, white band reaching across the heavens. This band, upon closer observation, looks speckled and dusty, filled with a million tiny points of light and halos of glowing matter. What you are seeing is the Milky Way, something that astronomers and stargazers alike have been staring up at since the beginning of time.
But just what is the Milky Way? Well, simply put, it is the name of the barred spiral galaxy in which our solar system is located. The Earth orbits the Sun in the Solar System, and the Solar System is embedded within this vast galaxy of stars. It is just one of hundreds of billions of galaxies in the Universe, and ours is called the Milky Way because the disk of the galaxy appears to be spanning the night sky like a hazy band of glowing white light. Continue reading “What is the Milky Way?”
Illustration of the Kepler spacecraft. Kepler's mission is over, but all of the exoplanets it found still need to be confirmed in follow-up observations. (NASA/Kepler mission/Wendy Stenzel)
Kepler may not be hanging up its planet-hunting hat just yet. Even though two of its four reaction wheels — which are crucial to long-duration observations of distant stars — are no longer operating, it could still be able to seek out potentially-habitable exoplanets around smaller stars. In fact, in its new 2-wheel mode, Kepler might actually open up a whole new territory of exoplanet exploration looking for Earth-sized worlds orbiting white dwarfs.
An international team of scientists, led by Mukremin Kilic of the University of Oklahoma’s Department of Physics and Astronomy, are suggesting that NASA’s Kepler spacecraft should turn its gaze toward dim white dwarfs, rather than the brighter main-sequence stars it was previously observing.
“A large fraction of white dwarfs (WDs) may host planets in their habitable zones. These planets may provide our best chance to detect bio-markers on a transiting ex- oplanet, thanks to the diminished contrast ratio between the Earth-sized WD and its Earth-sized planets. The James Webb Space Telescope is capable of obtaining the first spectroscopic measurements of such planets, yet there are no known planets around WDs. Here we propose to take advantage of the unique capability of the Kepler space- craft in the 2-Wheels mode to perform a transit survey that is capable of identifying the first planets in the habitable zone of a WD.”
– Kilic et al.
Any bio-markers — such as molecular oxygen, O2 — could later be identified around such Earth-sized exoplanets by the JWST, they propose.
Will Kepler be able to find the first Earth-sized exoplanet — or even an exomoon — orbiting a white dwarf? (Illustration of Kepler 22b. Credit: NASA/Ames/JPL-Caltech)
Because Kepler’s precision has been greatly reduced by the failure of a second reaction wheel earlier this year, it cannot accurately aim at large stars for the long periods of time required to identify the minute dips in brightness caused by the silhouetted specks of passing planets. But since white dwarfs — the dim remains of stars like our Sun — are much smaller, any eclipsing exoplanets would make a much more pronounced effect on their apparent luminosity.
In effect, exoplanets ranging from Earth- to Jupiter-size orbiting white dwarfs as close as .03 AU — well within their habitable zones — would significantly block their light, making Kepler’s diminished aim not so much of an issue.
“Given the eclipse signature of Earth-size and larger planets around WDs, the systematic errors due to the pointing problems is not the limiting factor for WDHZ observations,” the team assures in their paper “Habitable Planets Around White Dwarfs: an Alternate Mission for the Kepler Spacecraft.”
Even smaller orbiting objects could potentially be spotted in this fashion, they add… perhaps even as small as the Moon.
The team is proposing a 200-day-long survey of 10,000 known white dwarfs within the Sloan Digital Sky Survey (SDSS) area, and expects to find up to 100 exoplanet candidates as well as other “eclipsing short period stellar and sub-stellar companions.”
“If the history of exoplanet science has taught us anything, it is that planets are ubiquitous and they exist in the most unusual places, including very close to their host stars and even around pulsars… Currently there are no known planets around WDs, but we have never looked at a sufficient number of WDs at high cadence to find them through transit observations.”
NASA’s Ames Research Center made an open call for proposals regarding Kepler’s future operations on August 2. Today is the due date for submissions, which will undergo a review process until Nov. 1, 2013.
Added 9/4: For another take on this, check out Paul Gilster’s write-up on Centauri Dreams.
Here’s our Weekly Space Hangout for July 19, 2013. Watch as a team of space and astronomy journalists discuss the big space stories of the week. We do this every Friday at 12:00 pm Pacific Time / 3:00 pm Eastern Time. You can join us live, or watch the archive here or on Google+.
Comet ISON seen against a background of stars and galaxies (Source: /hubblesite.org)
This image of the steadily-approaching Comet ISON, made from observations with the Hubble Space Telescope on April 30, show not only the comet itself but also a rich background of stars located within our own galaxy and even the distant spirals of entire galaxies much, much farther away — as Josh Sokol describes it on HubbleSite.org’s ISONblog it’s like the astronomy stickers you’d get for your kid’s bedroom, except you’d never get to see such a scene in real life “unless, of course, you had Hubble.”
Comet C/2012 S1 (ISON) is currently on its way into the inner Solar System on course for a close encounter with the Sun, zooming along at 77,250 km/h (48,000 miles per hour). It will make its closest pass by the Sun on November 28 (coming within just .012 AU) and will hopefully put on a pretty spectacular show in the night sky — especially if it survives the trip.
Comet ISON’s projected path through the night sky prior to perihelion. (Credit: NASA/GSFC/Axel Mellinger)
The image above was created from multiple Hubble observations earlier this year, some geared toward capturing ISON and others calibrated more for distant, dimmer objects like galaxies and far-flung stars. By combining the results we get a view of a comet speeding through space with an almost too-perfect hyperrealism, courtesy of NASA’s hardest-working space telescope.
“The result is part science, part art. It’s a simulation of what our eyes, with their ability to dynamically adjust to brighter and fainter objects, would see if we could look up at the heavens with the resolution of Hubble. The result is a hodepodge of almost all the meat-and-potatoes subjects of astronomy – no glow-in-the-dark stickers required.”
When we look at the night sky, filled with stars, it’s hard to resist counting. Just with the unaided eye, in dark skies, you can see a few thousand.
How many stars are there in the entire Universe? Before we get to that massive number, let’s consider what you can count with the tools available to you.
Perfect vision in dark skies allows us to see stars down to about magnitude 6. But to really make an accurate census of the total number of stars, you’d need to travel to both the Northern and Southern Hemispheres, since only part of the sky is visible from each portion of the Earth. Furthermore, you’d need to make your count over several months, since a portion of the sky is obscured by the Sun. If you had perfect eyesight and traveled to completely dark skies in both the Northern and Southern Hemispheres, and there was no Moon, you might be able to get to count up almost 9,000 stars.
With a good pair of binoculars, that number jumps to about 200,000, since you can observe stars down to magnitude 9. A small telescope, capable of resolving magnitude 13 stars will let you count up to 15 million stars. Large observatories could resolve billions of stars.
But how many stars are out there? How many stars are there in the Milky Way?
Milky Way. Image credit: NASA
According to astronomers, our Milky Way is an average-sized barred spiral galaxy measuring up to 120,000 light-years across. Our Sun is located about 27,000 light-years from the galactic core in the Orion arm. Astronomers estimate that the Milky Way contains up to 400 billion stars of various sizes and brightness.
A few are supergiants, like Betelgeuse or Rigel. Many more are average-sized stars like our Sun. The vast majority of stars in the Milky Way are red dwarf stars; dim, low mass, with a fraction of the brightness of our Sun.
As we peer through our telescopes, we can see fuzzy patches in the sky which astronomers now know are other galaxies like our Milky Way. These massive structures can contain more or less stars than our own Milky Way.
Elliptical galaxy ESO 325-G004. ESO
There are spiral galaxies out there with more than a trillion stars, and giant elliptical galaxies with 100 trillion stars.
And there are tiny dwarf galaxies with a fraction of our number of stars.
So how many galaxies are there?
According to astronomers, there are probably more than 170 billion galaxies in the observable Universe, stretching out into a region of space 13.8 billion light-years away from us in all directions.
And so, if you multiply the number of stars in our galaxy by the number of galaxies in the Universe, you get approximately 1024 stars. That’s a 1 followed by twenty-four zeros.
That’s a septillion stars.
But there could be more than that.
It’s been calculated that the observable Universe is a bubble of space 47 billion years in all directions.
It defines the amount of the Universe that we can see, because that’s how long light has taken to reach us since the Big Bang.
This is a minimum value, the Universe could be much bigger – it’s just that we can’t ever detect those stars because they’re outside the observable Universe. It’s even possible that the Universe is infinite, stretching on forever, with an infinite amount of stars. So add a couple more zeros. Maybe an infinite number of zeroes.
A new view of the spectacular stellar nursery IC 2944 (ESO)
This Saturday will mark 15 years that the European Southern Observatory’s Very Large Telescope (VLT) first opened its eyes on the Universe, and ESO is celebrating its first-light anniversary with a beautiful and intriguing new image of the stellar nursery IC 2944, full of bright young stars and ink-black clouds of cold interstellar dust.
This is the clearest ground-based image yet of IC 2944, located 6,500 light-years away in the southern constellation Centaurus.
Emission nebulae like IC 2944 are composed mostly of hydrogen gas that glows in a distinctive shade of red, due to the intense radiation from the many brilliant newborn stars. Clearly revealed against this bright backdrop are mysterious dark clots of opaque dust, cold clouds known as Bok globules. They are named after Dutch-American astronomer Bart Bok, who first drew attention to them in the 1940s as possible sites of star formation. This particular set is nicknamed the Thackeray Globules.
Larger Bok globules in quieter locations often collapse to form new stars but the ones in this picture are under fierce bombardment from the ultraviolet radiation from nearby hot young stars. They are both being eroded away and also fragmenting, like lumps of butter dropped into a hot frying pan. It is likely that Thackeray’s Globules will be destroyed before they can collapse and form stars.
This new picture celebrates an important anniversary for the the VLT – it will be fifteen years since first light on the first of its four Unit Telescopes on May 25, 1998. Since then the four original giant telescopes have been joined by the four small Auxiliary Telescopes that form part of the VLT Interferometer (VLTI) – one of the most powerful and productive ground-based astronomical facilities in existence.
The selection of images below — one per year — gives a taste of the VLT’s scientific productivity since first light in 1998:
A selection of images from 15 years of the VLT (Credits: ESO/P.D. Barthel/M. McCaughrean/M. Andersen/S. Gillessen et al./Y. Beletsky/R. Chini/T. Preibisch)
Read more on the ESO site here, and watch an ESOCast video below honoring the VLT’s fifteen-year milestone:
If you couldn’t tell, we love time-lapse videos… whether they’re made of photos looking up at the sky from Earth or looking down at Earth from the sky! This latest assembly by photographer Bruce W. Berry takes us on a tour around the planet from orbit, created from images taken by astronauts aboard the International Space Station and expertly de-noised, stabilized and smoothed to 24 frames per second. The result is — like several others before — simply stunning, a wonderful reminder of our place in space and the beauty of our living world.
Hubble image of SNR 0519, the remains of a Type Ia supernova in the Large Magellanic Cloud
Stars like our Sun can last for a very long time (in human terms, anyway!) somewhere in the neighborhood of 10-12 billion years. Already over 4.6 billion years old, the Sun is entering middle age and will keep on happily fusing hydrogen into helium for quite some time. But eventually even stars come to the end of their lives, and their deaths are some of the most powerful — and beautiful — events in the Universe.
The wispy, glowing red structures above are the remains of a white dwarf in the neighboring Large Magellanic Cloud 150,000 light-years away. Supernova remnant SNR 0519 was created about 600 years ago (by our time) when a star like the Sun, in the final stages of its life, gathered enough material from a companion to reach a critical mass and then explode, casting its outer layers far out into space to create the cosmic rose we see today.
As the hydrogen material from the star plows outwards through interstellar space it becomes ionized, glowing bright red.
SNR 0519 is the result of a Type Ia supernova, which are the result of one white dwarf within a binary pair drawing material onto itself from the other until it undergoes a core-collapse and blows apart violently. The binary pair can be two white dwarfs or a white dwarf and another type of star, such as a red giant, but at least one white dwarf is thought to always be the progenitor.
A recent search into the heart of the remnant found no surviving post-main sequence stars, suggesting that SNR 0519 was created by two white dwarfs rather than a mismatched pair. Both stars were likely destroyed in the explosion, as any non-degenerate partner would have remained.
This image of Cep OB 3b was created by combining the light from four separate observations taken through different filters on the 0.9 meter telescope at Kitt Peak. The brightest yellow star near the center of the image is a foreground star, lying between us and the young cluster. The other bright stars are the massive young stars of the cluster that are heating the gas and dust in the cloud and blowing out cavities. Image processing was done by Dr. Travis Rector. Credit: NOAO.
It takes time to understand the life of stars. A star like our Sun takes tens of millions of years to form, and so much like archeologists who reconstruct ancient cities from shards of debris strewn over time, astronomers must reconstruct the birth process of stars indirectly, by observing stars in different stages of the process and inferring the changes that take place.
One of the best places to study the lives of stars is in star clusters. These regions that are rich with young stars provide astronomers much information that is relevant to the study of stars in general, but within a cluster, stars can form during a wide range of time, as a new study of the star cluster named Cep OB3b has shown.
“By studying nearby massive young clusters like Cep OB3b, we can gain a greater understanding of the environments out of which planets form,” said Thomas Allen from the University of Toledo, who is one of the authors of the new paper.
Located in the northern constellation of Cepheus, CepOB3b is similar in some ways to the famous cluster found in the Orion Nebula. But unlike the Orion Nebula, there is relatively little dust and gas obscuring our view of Cep OB3b. Its massive, hot stars have blown out cavities in the gaseous cloud with their intense ultraviolet radiation which mercilessly destroys everything in its path. Cep OB3b may show us what the Orion Nebular Cluster will look like in the future.
Allen and an international team of astronomers have found that the total number of young stars in the cluster is as high as 3,000. Infrared observations of the stars from the NASA Spitzer satellite show about 1,000 stars that are surrounded by disks of gas and dust from which solar systems may form. As the stars age, the disks disappear as the dust and gas get converted into planets or are dispersed into space.
But these observations pointed to a new mystery. Although the stars in Cep OB3b are thought to be about three million years old, in some parts of the cluster most of the stars had lost their disks, suggesting that the stars in those parts were older. This suggests that the cluster is surrounded by older stars, potential relics of previous clusters that have since expanded and dispersed.
To search for evidence for these relic clusters, Allen used the Mosaic camera on the 0.9 meter telescope at Kitt Peak National Observatory to observe wide field images of CepOB3b. These images show hot gas and its interaction with the stars and permit the team to study a curious cavity in the gas for evidence of older, yet still juvenile, stars that have lost their disks of gas and dust.
With these data, the team is searching for the previous generations of star formation in the region surrounding Cep OB3b, and piecing together the history of star formation in this magnificent region. When finished, this may provide clues how previous generations may have influenced the current generation of stars and planets forming in Cep OB3b.
Vistas of Many Worlds: A Journey Through Space and Time by Erik Anderson (Ashland Astronomy Studio)
While many astronomy books are based around images that show us how the Universe appears to us right now, as seen through the sensitive electronic eyes of powerful space telescopes and observatories around the world, Erik Anderson’s Vistas of Many Worlds: a Journey Through Space and Time takes a different, but no less fascinating, approach and shows us what the night sky used to look like, will one day look like, and how it may look from other much more distant worlds.
The nearby orange dwarf star Epsilon Eridani reveals its circumstellar debris disks in this close-up perspective. (Pages 14-15)
Written and illustrated by Erik Anderson of the Ashland Astronomy Studio in Ashland, Oregon, Vistas of Many Worlds first takes us on a tour of our local region of the galaxy, introducing us to some of our Sun’s closest neighbors in space. From Alpha Centauri to Altair, we get scientifically-based renderings of several nearby stars as they’d appear close up, along with a detailed description of each — as well as an accurate depiction of the background stars (including the Sun) as they’d appear from such slightly different vantage points. We soon find out there’s an amazing amount of variety in our own stellar neighborhood alone!
Next we get a tour through time itself with images and detailed descriptions of the night sky as it appeared at various points in Earth’s history. Based on the actual movements of the stars across the galaxy, Anderson is able to accurately show the star-filled sky as it looked when the ocean cascaded over the Strait of Gibraltar to fill in the Mediterranean 5.3 million years ago, when the ancestors of modern humans were first learning to use fire 1.5 million years ago… and also what it will look like when the Solar System eventually dips back down into the galactic plane 25 million years from now — a time when nearly all the stars in the sky will be strangers, unfamiliar to us today.
After that Anderson takes us on a hunt for exoplanets, both known and imagined. We first visit the star systems that have been recently discovered to host planets — some a little like Earth, some a little like Jupiter, and some like nothing we’ve ever seen before. Then it’s off to look for truly Earthlike worlds by looking back at how our own planet became so favorable for life in the first place. From a stable parent star like the Sun to the chance birth of a large, stabilizing moon, from the delivery of life-sustaining liquid water (that stays liquid!) to having a protective “big brother” gas giant ready to take the heavy hits, and eventually what first drew organisms up from the sea onto dry land, Anderson speculates about Earth’s distant exoplanetary twins by reflecting on our planet itself.
The Earth’s ancient past is depicted as it looked 4.4 million years ago when an ancient ape, “Ardi” the Ardipithecus, roamed Africa. (Pages 36-37)
And all the while showing what stars are where in the sky.
Vistas of Many Worlds is a true gem… it inspires imagination with the turn of each page. Anderson’s photorealistic computer-generated illustrations are lush and intriguing, and he does an excellent job combining speculation with scientific knowledge. It’s science as envisioned by an artist as well as art created by a scientist — truly the best of both many worlds.
A primordial ocean-world orbited by two moons is depicted in Ptolemy’s Cluster (star cluster M7). The scene parallels Earth’s own natural history, commemorating the origins of watery oceans out of volcanic steam and infalling comets. (Pages 96-97)
