Stars: A Day in the Life

There is something about them that intrigues us all. These massive spheres of gas burning intensely from the energy of fusion buried many thousands of kilometers deep within their cores. The stars have been the object of humanity’s wonderment for as far back as we have records. Many of humanity’s religions can be tied to worshiping these celestial candles. For the Egyptians, the sun was representative of the God Ra, who each day vanquished the night and brought light and warmth to the lands. For the Greeks, it was Apollo who drove his flaming chariot across the sky, illuminating the world. Even in Christianity, Jesus can be said to be representative of the sun given the striking characteristics his story holds with ancient astrological beliefs and figures. In fact, many of the ancient beliefs follow a similar path, all of which tie their origins to that of the worship of the sun and stars.

 

Humanity thrived off of the stars in the night sky because they recognized a correlation in the pattern in which certain star formations (known as constellations) represented specific times in the yearly cycle. One of which meant that it was to become warmer soon, which led to planting food. The other constellations foretold the coming of a

The familiar constellation of Orion. Orion's Belt can be clearly seen, as well as Betelgeuse (red star in the upper left corner) and Rigel (bright blue star in the lower right corner) Credit: NASA Astronomy Picture of the Day Collection NASA
The familiar constellation of Orion. Orion’s Belt can be clearly seen, as well as Betelgeuse (red star in the upper left corner) and Rigel (bright blue star in the lower right corner)
Credit: NASA Astronomy Picture of the Day Collection
NASA

colder period, so you were able to begin storing food and gathering firewood. Moving forward in humanity’s journey, the stars then became a way to navigate. Sailing by the stars was the way to get around, and we owe our early exploration to our understandings of the constellations. For many of the tens of thousands of years that human eyes have gazed upwards toward the heavens, it wasn’t until relatively recently that we fully began to understand what stars actually were, where they came from, and how they lived and died. This is what we shall discuss in this article. Come with me as we venture deep into the cosmos and witness physics writ large, as I cover how a star is born, lives, and eventually dies.

We begin our journey by traveling out into the universe in search of something special. We are looking for a unique structure where both the right circumstances and ingredients are present. We are looking for what astronomer’s call a Dark Nebula. I’m sure you’ve heard of nebulae before, and have no doubt seen them. Many of the amazing images that the Hubble Space Telescope has obtained are of beautiful gas clouds, glowing amidst the backdrop of billions of stars. Their colors range from deep reds, to vibrant blues, and even some eerie greens. This is not the type of nebula we are in search of though. The nebula we need is dark, opaque, and very, very cold.

You may by wondering to yourself, “Why are we looking for something dark and cold when stars are bright and hot?”

http://www.eso.org/public/images/eso1501a/
Image of a Dark Nebula  Credit: ESO   http://www.eso.org/public/images/eso1501a

Indeed, this is something that would appear puzzling at first. Why does something need to be cold first before it can become extremely hot? First, we must cover something elementary about what we call the Interstellar Medium (ISM), or the space between the stars. Space is not empty as its name would imply. Space contains both gas and dust. The gas we are mainly referring to is Hydrogen, the most abundant element in the universe. Since the universe is not uniform (the same density of gas and dust over every cubic meter), there are pockets of space that contain more gas and dust than others. This causes gravity to manipulate these pockets to come together and form what we see as nebulae. Many things go into the making of these different nebulae, but the one that we are looking for, a Dark Nebula, possesses very special properties. Now, let us dive into one of these Dark Nebulae and see what is going on.

As we descend through the outer layers of this nebula, we notice that the temperature of the gas and dust is very low. In some nebulae, the temperatures are very hot. The more particles bump into each other, excited by the absorption and emission of exterior and interior radiation, means higher temperatures. But in this Dark Nebula, the opposite is happening. The temperatures are decreasing the further into the cloud we get. The reason these Dark Nebulae have specific properties that work to create a great stellar nursery has to deal with the basic properties of the nebula and the region type that the cloud exists in, which has some difficult concepts associated with it that I will not fully illustrate here. They include the region where the molecular clouds form which are called Neutral Hydrogen Regions, and the properties of these regions have to deal with electron spin values, along with magnetic field interactions that effect said electrons. The traits that I will cover are what allows for this particular nebula to be ripe for star formation.

Excluding the complex science behind what helps form these nebulae, we can begin to address the first question of why must we get colder to get hotter. The answer comes down to gravity. When particles are heated, or excited, they move faster. A cloud with sufficient energy will contain far too much momentum among each of the dust and gas particles for any type of formations to occur. As in, if dust grains and gas atoms are moving too quickly, they will simply bounce off of one another or just shoot past each other, never achieving any type of bond. Without this interaction, you can never have a star. However, if the temperatures are cold enough, the particles of gas and dust are moving so slow that their mutual gravity will allow for them to start to “stick” together. It is this process that allows for a protostar to begin to form.

Generally what supplies energy to allow for the faster motion of the particles in these molecular clouds is radiation. Of course, there is radiation coming in from all directions at all times in the universe. As we see with other nebulae, they are glowing with energy and stars aren’t being born amid these hot gas clouds. They are being heated by external radiation from other stars and from its own internal heat. How does this Dark Nebula prevent external radiation from heating up the gas in the cloud and causing it to move too fast for gravity to take hold? This is where

http://www.eso.org/public/images/eso0102a/
Barnard 68 is a large molecular cloud that is so thick, it blocks out the light from stars that we normally would be able to see.  Credit: ESO     http://www.eso.org/public/images/eso0102a

the opaque nature of these Dark Nebulae comes into play. Opacity is the measure of how much light is able to move through an object. The more material in the object or the thicker the object is, the less light is able to penetrate it. The higher frequency light (Gamma Rays, X-Rays, and UV) and even the visible frequencies are affected more by thick pockets of gas and dust. Only the lower frequency types of light, including Infrared, Microwaves, and Radio Waves, has any success of penetrating gas clouds such as these, and even it is somewhat scattered so that generally they do not contain nearly enough energy to begin to disrupt this precarious process of star formation. Thus, the inner portions of the dark gas clouds are effectively “shielded” from the outside radiation that disrupts other, less opaque nebulae. The less radiation that makes it into the cloud, the lower the temperatures of the gas and dust within it. The colder temperatures means less particle motion within the cloud, which is key for what we will discuss next.

Indeed, as we descend towards the core of this dark molecular cloud, we notice that less and less visible light makes it to our eyes, and with special filters, we can see that this is true of other frequencies of light. As a result, the cloud’s temperature is very low. It is worth noting that the process of star formation takes a very long time, and in the interest of not keeping you reading for hundreds of thousands of years, we shall now fast forward time. In a few thousand years, gravity has pulled in a fair amount of gas and dust from the surrounding molecular cloud, causing it to clump together. Dust and gas particles, still shielded from outside radiation, are free to naturally come together and “stick” at these low temperatures. Eventually, something interesting begins to happen. The mutual gravity of this ever growing ball of gas and dust begins a snowball (or star-ball) effect. The more layers of gas and dust that are coagulated together, the denser the interior of this protostar becomes. This density increases the gravitational force near the protostar, thus pulling more material into it. With every dust grain and hydrogen atom that it accumulates, the pressure in the interior of this ball of gas increases.

If you remember anything from any chemistry class you’ve ever taken, you may recall a very special relationship between pressure and temperature when dealing with a gas. PV=nRT, the Ideal Gas Law, comes to mind. Excluding the constant scalar value ‘n’ and the gas constant R ({8.314 J/mol x K}), and solving for Temperature (T), we get T=PV, which means that the temperature of a gas cloud is directly proportional to pressure. If you increase the pressure, you increase the temperature. The core of this soon-to-be star residing in this Dark Nebula is becoming very dense, and the pressure is skyrocketing. According to what we just calculated, that means that the temperature is also increasing.

NASA/JPL-Caltech/R. Hurt (SSC)
Artistic rendition of a star forming within a dark nebula. Credit: NASA/JPL-Caltech/R. Hurt (SSC)

 

We yet again consider this nebula for the next step. This nebula has a large amount of dust and gas (hence it being opaque), which means it has a lot of material to feed our protostar. It continues to pull in the gas and dust from its surrounding environment and begins heating up. The hydrogen particles in the core of this object are bouncing around so quick that they are releasing energy into the star. The protostar begins to get very hot and is now glowing with radiation (generally Infrared). At this point, gravity is still pulling in more gas and dust which is adding to the pressures exerted deep within the core of this protostar. The gas of the Dark Nebula will continue to collapse in on itself until something important happens. When there is little to nothing left near the star to fall onto its surface, it begins to lose energy (due to it radiating away as light). When this happens, that outward force lessens and gravity starts to contract the star faster. This greatly increases the pressure in the core of this protostar. As the pressure grows, the temperature in the core reaches a value that is crucial for the process that we are witnessing. The protostar’s core has become so dense and hot, that it reaches roughly 10 million Kelvin. To put that into perspective, this temperature is roughly 1700x hotter than the surface of our sun (at around 5800K). Why is 10 million Kelvin so important? Because at that temperature, the thermonuclear fusion of Hydrogen can occur, and once fusion starts, this newborn star “turns on” and bursts to life, sending out vast amounts of energy in all directions.

In the core, it is so hot that the electrons that zip around the hydrogen’s proton nuclei are stripped off (ionized), and all you have are free moving protons. If the temperature isn’t hot enough, these free flying protons (which have positive charges), will simply glance off one another. However, at 10 Million Kelvin, the protons are moving so fast that they can get close enough to allow for the Strong Nuclear Force to take over, and when it does the Hydrogen protons begin slamming into each other with enough force to fuse together, creating Helium atoms and releasing lots of energy in the form of radiation. It’s a chain reaction that can be summed up as 4 Protons yield 1 Helium atom + energy. This fusion is what ignites the star and causes it to “burn”. The energy liberated by this reaction goes into helping other Hydrogen protons fuse and also supplies the energy to keep the star from collapsing in on itself. The energy that is pumping out of this star in all directions all comes from the core, and the subsequent layers of this young star all transmit that heat in their own way (using radiation and convection methods depending upon what type of star has been born).

Newborn stars glow through their parent molecular cloud Credit: ESA/Hubble & NASA Acknowledgement: Judy Schmidt
Newborn stars glow through their parent molecular cloud
Credit: ESA/Hubble & NASA Acknowledgement: Judy Schmidt

What we have witnessed now, from the start of our journey when we dove down into that cold Dark Nebula, is the birth of a young, hot star. The nebula protected this star from errant radiation that would have disrupted this process, as well as providing the frigid environment that was needed for gravity to take hold and work its magic. As we witnessed the protostar form, we may also have seen something incredible. If the contents of this nebula are right, such as having a high amount of heavy metals and silicates (left over from the supernovae of previous, more massive stars) what we could begin to see would be planetary formation taking place in the accretion disk of material around the protostar.

Remaining gas and dust in the vicinity of our new star would begin to form dense pockets by the same mechanism of

Artistic rendition of a protoplanet forming within the accretion disk of a protostar Credit: ESO/L. Calçada http://www.eso.org/public/images/eso1310a/
Artistic rendition of a protoplanet forming within the accretion disk of a protostar
Credit: ESO/L. Calçada
http://www.eso.org/public/images/eso1310a/

gravity, eventually being able to accrete into protoplanets that will be made up of gas or silicates and metal (or a combination of the two). That being said, planetary formation is still somewhat a mystery to us, as there seems to be things that we cannot explain yet at work. But this model of star system formation seems to work well.

The life of the star isn’t nearly as exciting as its birth or death. We will continue to fast forward the clock and watch this star system evolve. Over a few billion years, the remnants of the Dark Nebula have been blown apart and have also formed other stars like the one we witnessed, and it no longer exists. The planets we saw being formed as the protostar grew begin their billion year dance around their parent star. Maybe on one of these worlds, a world that sits at just the right distance away from the star, liquid water exists. Within that water contains the amino acids that are needed for proteins (all composed of the elements that were left over by previous stellar eruptions). These proteins are able to link together to start to form RNA chains, then DNA chains. Maybe at one point a few billion years after the star has been born, we see a space-faring species launch itself into the cosmos, or perhaps they never achieve this for various reasons and remain planet-bound. Of course this is just speculation for our amusement. However, now we come to the end of our journey that began billions of years ago. The star begins to die.

The Hydrogen in its core is being fused into Helium, which depletes the Hydrogen over time; the star is running out of gas. After many years, the hydrogen fusion process begins to stop, and the star puts out less and less energy. This lack of outward pressure from the fusion process upsets what we call the hydrostatic equilibrium, and allows gravity (which is always trying to crush the star) to win. The star begins to shrink rapidly under its own weight. But, just as we discussed earlier, as the pressure increases, so too does the temperature. All of that Helium that was left over

Inward force of gravity versus the outward pressure of fusion within a star (hydrostatic equilibrium) Credit: NASA
Inward force of gravity versus the outward pressure of fusion within a star (hydrostatic equilibrium)
Credit: NASA

from the billions of years of hydrogen fusion now begins to heat up in the core. Helium fuses at a much hotter temperature than Hydrogen does, which means that the Helium rich core is able to be pressed inward by gravity without fusing (yet). Since fusion isn’t occurring in the Helium core, there is little to no outward force (given off by fusion) to prevent the core from collapsing. This matter becomes much denser, which we now label as degenerate, and is pushing out massive amounts of heat (gravitational energy becoming thermal energy). This causes the remaining Hydrogen that is in subsequent layers above the Helium core to fuse, which causes the star to expand greatly as this Hydrogen shell burns out of control. This makes the star “rebound” and it expands rapidly; the more energetic fusion from the Hydrogen shells outside of the core expanding the diameter of the star greatly. Our star is now a red giant. Some, if not all of the inner planets that we witnessed form will be incinerated and swallowed up by the star that first gave them life. If there happened to be any life on any of those planets that didn’t manage to leave their home world, they would certainly be erased from the universe, never to be known of.

This process of the star running out of fuel (first Hydrogen, then Helium, etc…) will continue for a while. Eventually, the Helium in the core will reach a certain temperature and begin to fuse into Carbon, which will put off the collapse (and death) of the star. The star we are currently watching live and die is an average-sized Main Sequence Star, so its life ends once it is finished fusing Helium into

Different planetary nebulae, all remnants of low mass stars ejecting their outer material as they die Credit: NASA
Different planetary nebulae, all remnants of low mass stars ejecting their outer material as they die
Credit: NASA

Carbon. If the star was much larger, this fusion process would proceed until we reached Iron. Iron is the element in which fusion does not take place spontaneously, meaning it requires more energy to fuse it than it gives off after fusion. However, our star will never make it to Iron in its core, and thus it has died after it exhausts its Helium reservoir. When the fusion process finally “turns off” (out of gas), the star slowly begins to cool and the outer layers of the star expand and are ejected into space. Subsequent ejections of stellar material proceed to create what we call a planetary nebula, and all that is left of the once brilliant star we watched spring into existence is now just a ball of dense carbon that will continue to cool for the rest of eternity, possibly crystallizing into diamond.

 

The death we witnessed just now isn’t the only way a star dies. If a star is sufficiently large enough, its death is much more violent. The star will erupt into the largest explosion in the universe, called a supernova. Depending on many variables, the remnant of the star could end up as a neutron star, or even a black hole. But for most of what we call the average sized Main Sequence Stars, the death that we witnessed will be their fate.

Artistic representation of the material around the supernova 1987A. Credit: ESO/L. Calçada
Artistic representation of the material around the supernova 1987A. Supernovae are among the most violent events in the universe
Credit: ESO/L. Calçada

Our journey ends with us pondering what we have observed. Seeing just what nature can do given the right circumstances, and watching a cloud of very cold gas and dust turn into something that has the potential to breathe life into the cosmos. Our minds wander back to that species that could have evolved on one of those planets. You think about how they may have gone through phases similar to us. Possibly using the stars as supernatural deities that guided their beliefs for thousands of years, substituting answers in for where their ignorance reigned. These beliefs could possibly turn into religions, still grasping that notion of special selection and magnanimous thought. Would the stars fuel their desire to understand the universe as the stars did for us? Your mind then ponders what our fate will be if we do not attempt to take the next step into the universe. Are we to allow our species to be erased from the cosmos as our star expands in its death? This journey you just made into the heart of a Dark Nebula truly exemplifies what the human mind can do, and shows you just how far we have come even though we are still bound to our solar system. The things you have learned were found by others like you simply asking how things occur and then bringing the full weight of our knowledge of physics to bare. Imagine what we can accomplish if we continue this process; being able to fully achieve our place among the stars.

The vastness of space awaits us... Credit: NASA
The vastness of the cosmos awaits us…
Credit: NASA (Hubble Deep Field)

Astrophotos: A Wide Angle “Trilogy” of the North America Nebula

A perfect set of astrophotos for #WideAngleWednesday! Here are not one but three views of the North America Nebula taken by Terry Hancock. Terry said this is his widest view yet of this region. Also known as NGC 7000 or Caldwell 20, this is an emission nebula in the constellation Cygnus that resembles the shape of North America and The Gulf Of Mexico. It lies at a distance of approximately 1800 light years away from Earth.

Terry presents a “trilogy” of three different color processes (see below). He took imagery in both July and September 2014 with a total exposure time of 13.9 hours from his Down Under Observatory in Fremont, Michigan.

For more details about the processing for each image, click on the images. To see more of Terry’s great work, see his website, Facebook, Flickr, or G+.

A wide, three-panel mosaic spanning an area approximately 2.5 x 5.5 degrees of the North America Nebula (NGC 7000 or Caldwell 20), in H-Alpha, Hubble Palette and RGB with H-Alpha. Credit and copyright: Terry Hancock.
A wide, three-panel mosaic spanning an area approximately 2.5 x 5.5 degrees of the North America Nebula (NGC 7000 or Caldwell 20), in H-Alpha, Hubble Palette and RGB with H-Alpha. Credit and copyright: Terry Hancock.
Another version of the 3-panel, wide angle view of the North America Nebula. Credit and copyright: Terry Hancock.
Another version of the 3-panel, wide angle view of the North America Nebula. Credit and copyright: Terry Hancock.

Want to get your astrophoto featured on Universe Today? Join our Flickr group or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.

Virtual Star Party – October 6, 2013

Another wonderful Virtual Star Party, this time with 6 astronomers broadcasting their view of the night sky live. We had amazing views of Saturn, the Ring Nebula, M27,  and M17 the Swan Nebula (also known as the Lobster or Horseshoe Nebula). We also caught great views of NGC-896, NGC-869, and the M56 Cluster. Then we got some beautiful views of the Veil Nebula and discussed the benefits of image-stabilized binoculars.

This was also the first time were joined by Scott Ferguson, who delighted us with his dark sky views from the west coast of Florida. His views of the Pelican Nebula (NGC-6996) were gorgeous and unique.
Continue reading “Virtual Star Party – October 6, 2013”

Weekly SkyWatcher’s Forecast: August 6-12, 2012

Greetings, fellow SkyWatchers! While you start your observing week out by watching the Mars Curiosity Landing, be sure to step outside and view the Aquarid meteor shower, too! It’s going to be a grand week for globular cluster studies and breezing along the Milky Way. Whenever you’re ready to learn some more history, mystery and just plain fun things about the night sky, then meet me in the back yard.

Monday, August 6 – Today in 2001 the Galileo spacecraft made its flyby of Jupiter’s moon – Io -sending back incredible images of the surface. For southern hemisphere observers, be on watch as the Iota Aquarid meteor shower peaks on this Universal date.

Tonight our studies of globular clusters continues as we look deeper into structure. As a rule, globular clusters normally contain a large number of variable stars, and most are usually the RR Lyrae type such as in earlier study M54. At one time they were known as “cluster variables,” with their number differing from one globular to another. Many globulars also contain vast numbers of white dwarfs. Some have neutron stars which are detected as pulsars, but out of all 151, only four have planetary nebulae in them.

Now, let us head toward the emerging constellation of Pegasus and the magnitude 6.5, class IV M15 (Right Ascension: 21 : 30.0 – Declination: +12 : 10). Easily located with even small binoculars about four degrees northwest of Enif, this magnificent globular cluster is a true delight in a telescope. Amongst the globulars, M15 ranks third in variable star population with 112 identified. As one of the densest of clusters, it is surprising that it is considered to be only class III. Its deeply concentrated core is easily apparent, and has begun the process of core collapse. The central core itself is very small compared to the cluster’s true size and almost half M15?s mass is contained within it. Although it has been studied by the Hubble, we still do not know if this density is caused by the cluster stars’ mutual gravity, or if it might disguise a supermassive object similar to those in galactic nuclei.

M15 was the first globular cluster in which a planetary nebula, known as Pease 1, could be identified. Larger aperture scopes can easily see it at high power. Surprisingly, M15 also is home to 9 known pulsars, which are neutron stars left behind from previous supernovae during the cluster’s evolution, and one of these is a double neutron star. While total resolution is impossible, a handful of bright stars can be picked out against that magnificent core region and wonderful chains and streams of members await your investigation tonight!

Tuesday, August 7 – On this date in 1959, Explorer 6 became the first satellite to transmit photographs of the Earth from its orbit.

Tonight, let’s return again to look at two giant globular clusters roughly equal in size, but not equal in class. To judge them fairly, you must use the same eyepiece. Start first by re-locating previous study M4. This is a class IX globular cluster. Notice the powder-like qualities. It might be heavily populated, but it is not dense. Now return to previous study M13. This is a class V globular cluster. Most telescopes will make out at least some resolution and a distinct core region. It is the level of condensation that determines the class. It is no different from judging magnitudes and simply takes practice.

Try your hand at M55 (Right Ascension:19 : 40.0 – Declination: -30 : 58) along the bottom of the Sagittarius “teapot” – it’s a class XI. Although it is a full magnitude brighter than class I M75, which we looked at earlier in the week, can you tell the difference in concentration? For those with GoTo systems, take a quick hop through Ophiuchus and look at the difference between NGC 6356 (class II) and NGC 6426 (class IX). If you want to try one that they can’t even classify? Look no further than M71 (Right Ascension: 19 : 53.8 – Declination: +18 : 47) in Sagitta. It’s all a wonderful game and the most fun comes from learning!

In the meantime, don’t forget all those other wonderful globular clusters such as 47 Tucanae, Omega Centauri, M56, M92, M28 and a host of others!

Wednesday, August 8 – Today in 2001, the Genesis Solar Particle Sample Return mission was launched. In September of 2004, it crash landed in the Utah desert with its precious payload. Although some of the specimens were contaminated, some did survive the mishap. So what is “star stuff?” Mostly highly charged particles generated from a star’s upper atmosphere and flowing out in a state of matter known as plasma…

Tonight let’s study one of the grandest of all solar winds as we seek out an area about three fingerwidths above the Sagittarius “teapot’s spout” as we have a look at magnificent M8 (Right Ascension: 18 : 03.8 – Declination: -24 : 23), the “Lagoon Nebula.”

Visible to the unaided eye as a hazy spot in the Milky Way, fantastic in binoculars, and an area truly worth study in any size scope, this 5200 light-year area of emission, reflection and dark nebulae has a rich history. Its involved star cluster – NGC 6530 – was first discovered by Flamsteed around 1680, and the nebula by Le Gentil in 1747. Cataloged by Lacaille as III.14 about 12 years before Messier listed it as number 8, its brightest region was recorded by John Herschel and the dark nebulae were discovered by Barnard.

Tremendous areas of starbirth are taking place in this region; while young, hot stars excite the gases in a are known as the “Hourglass,” around Herschel star 36 and 9 Sagittarius. Look closely around cluster NGC 6530 for Barnard dark nebulae B89 and B296 at the nebula’s southern edge. No matter how long you chose to swim in the “Lagoon” you will sure find more and more things to delight both the mind and the eye!

Thursday, August 9 – Today in 1976, the Luna 24 mission was launched on a return mission of its own – not to retrieve solar winds samples, but lunar soil! Remember this mission as we take a look at its landing site in the weeks ahead.

Tonight we’ll return to the nebula hunt as we head about a fingerwidth north and just slightly west of M8 for the “Trifid”…

M20 (Right Ascension: 18 : 02.3 – Declination: -23 : 02) was discovered by Messier on June 5, 1764, and much to his credit, he described it as a cluster of stars encased in nebulosity. This is truly a wonderful observation since the Trifid could not have been easy given his equipment. Some 20 years later William Herschel (although he usually avoided repeating Messier objects) found M20 of enough interest to assign separate designations to parts of this nebula – IV.41, V.10, V.11, V.12. The word “Trifid” was used to describe its beauty by John Herschel.

While M20 is a very tough call in binoculars, it is not impossible with good conditions to see the light of an area that left its home nearly a millennium ago. Even smaller scopes will pick up this round, hazy patch of both emission and reflection, but you will need aversion to see the dark nebula which divides it. This was cataloged by Barnard as B85. Larger telescopes will find the Trifid as one of the very few objects that actually appears much in the eyepiece as it does in photographs – with each lobe containing beautiful details, rifts and folds best seen at lower powers. Look for its cruciform star cluster and its fueling multiple system while you enjoy this triple treat tonight!

Friday, August 10 – Today in 1966 Lunar Orbiter 1 was successfully launched on its mission to survey the Moon. In the weeks ahead, we’ll take a look at what this mission sent back!

Tonight we’ll look at another star forming region as we head about a palm’s width north of the lid star (Lambda) in the Sagittarius teapot as we seek out “Omega”…

Easily viewed in binoculars of any size and outstanding in every telescope, the 5000 light-year distant Omega Nebula was first discovered by Philippe Loys de Cheseaux in 1745-46 and later (1764) cataloged by Messier as object 17. This beautiful emission nebula is the product of hot gases excited by the radiation of newly born stars. As part of a vast region of interstellar matter, many of its embedded stars don’t show in photographs, but reveal themselves beautifully to the eye of the telescope. As you look at its unique shape, you realize that many of these areas are obscured by dark dust, and this same dust is often illuminated by the stars themselves.

Often known as the “Swan,” M17 (Right Ascension: 18 : 20.8 – Declination: -16 : 11) will appear as a huge, glowing check mark or ghostly “2? in the sky – but power up if you use a larger telescope and look for a long, bright streak across its northern edge, with extensions to both the east and north. While the illuminating stars are truly hidden, you will see many glittering points in the structure itself and at least 35 of them are true members of this region spanning about 40 light-years that could contain up to 800 solar masses. It is awesome…

Saturday, August 11 – On this date in 1877, Asaph Hall of the U.S. Naval Observatory was very busy. This night would be the first time he would see Mars’ outer satellite Deimos! Six nights later, he observed Phobos, giving Mars its grand total of two moons.

Tonight after midnight is the peak of the Perseid meteor shower, and this year there’s not so much Moon to contend with! Now let’s sit back and talk about the Perseids while we watch…

The Perseids are undoubtedly the most famous of all meteor showers and never fail to provide an impressive display. Their activity appears in Chinese history as far back as 36 AD. In 1839, Eduard Heis was the first observer to give an hourly count, and discovered their maximum rate was around 160 per hour at that time. He, and other observers, continued their studies in subsequent years to find that this number varied.

Giovanni Schiaparelli was the first to relate the orbit of the Perseids to periodic comet Swift-Tuttle (1862 III). The fall rates have both risen and fallen over the years as the Perseid stream was studied more deeply, and many complex variations were discovered. There are actually four individual streams derived from the comet’s 120 year orbital period which peak on slightly different nights, but tonight through tomorrow morning at dawn is our accepted peak.

Meteors from this shower enter Earth’s atmosphere at a speed of 60 km/sec (134,000 miles per hour), from the general direction of the border between the constellations Perseus and Cassiopeia. While they can be seen anywhere in the sky, if you extend their paths backward, all the true members of the stream will point back to this region of the sky. For best success, position yourself so you are generally facing northeast and get comfortable. If you are clouded out, don’t worry. The Perseids will be around for a few more days yet, so continue to keep watch!

And speaking of watching… If you’re out late, be sure to watch for a Jupiter/Moon conjunction. What an inspiring bit of sky scenery to watch them rise together! For lucky viewers in the Indonesia area, this is an occultation event, so please be sure to check resources for times and locations in your area.

Sunday, August 12 – Did you mark your calendar to be up before dawn to view the Perseid meteor shower? Good!

Tonight while dark skies are on our side, we’ll fly with the “Eagle” as we hop another fingerwidth north of M17 and head for one of the most famous areas of starbirth – IC 4703.

While the open cluster NGC 6611 was first discovered by Cheseaux in 1745-6, it was Charles Messier who cataloged the object as M16 and he was the first to note the nebula IC 4703 (Right Ascension: 18 : 18.9 – Declination: -13 : 47), more commonly known as the “Eagle.” At 7000 light-years distant, this roughly 7th magnitude cluster and nebula can be spotted in binoculars, but at best it is a hint. As part of the same giant cloud of gas and dust as neighboring M17, the Eagle is also a place of starbirth illuminated by these hot, high energy stellar youngsters which are only about five and a half million years old.

In small to mid-sized telescopes, the cluster of around 20 brighter stars comes alive with a faint nebulosity that tends to be brighter in three areas. For larger telescopes, low power is essential. With good conditions, it is very possible to see areas of dark obscuration and the wonderful “notch” where the Pillars of Creation lie. Immortalized by the Hubble Space telescope, you won’t see them as grand or colorful as it did, but what a thrill to know they are there!

Until next week? Clear skies!

What Does a Nebula Sound Like?

What do things sound like out in the cosmos? Of course, sound waves can’t travel through the vacuum of space; however, electromagnetic waves can. These electromagnetic waves can be recorded by devices called spectrographs on many of the world’s most powerful telescopes. Astronomer Paul Francis from the Australian National University has used some of these recordings and converted them into sound by reducing their frequency 1.75 trillion times to make them audible, as the original frequencies are too high to be heard by the human ear.

“This allows us to listen to many parts of the universe for the first time,” Francis wrote on his website. “We can hear the song of a comet, the chimes of stars being born or dying, the choir of a quasar eating the heart of a galaxy, and much more.”
Continue reading “What Does a Nebula Sound Like?”

Spitzer’s Stunning New View of the North American Nebula

[/caption]

In visible light, the North American nebula resembles its namesake continent. But looking at it in the infrared spectrum, a whole new perspective explodes into view. Clouds of dust and gas come to life, as light from massive young star heats and shape the clouds, and dramatic clusters of baby stars which can only be seen in infrared burst into view.

“One of the things that makes me so excited about this image is how different it is from the visible image, and how much more we can see in the infrared than in the visible,” said Luisa Rebull of NASA’s Spitzer Science Center at the California Institute of Technology, Pasadena, Calif. Rebull is lead author of a paper about the observations, accepted for publication in the Astrophysical Journal Supplement Series. “The Spitzer image reveals a wealth of detail about the dust and the young stars here.”

Rebull and her team have identified more than 2,000 new, candidate young stars in the region. There were only about 200 known before. Because young stars grow up surrounded by blankets of dust, they are hidden in visible-light images. Spitzer’s infrared detectors pick up the glow of the dusty, buried stars.

This new view of the North American nebula combines both visible and infrared light observations, taken by the Digitized Sky Survey and NASA's Spitzer Space Telescope, respectively, into a single vivid picture. Image credit: NASA/JPL-Caltech

Combing infrared data with light from other parts of the spectrum gives astronomers a complete picture of star formation. Each different combination of observations gives insights into star formation.

But in Spitzer’s infrared view, the continent disappears. Instead, a swirling landscape of dust and young stars comes into view.

In this image, astronomers can see stars at all stages of life, from the early years when it is swaddled in dust to early adulthood, when it has become a young parent to a family of developing planets. Sprightly “toddler” stars with jets can also be identified in Spitzer’s view.

“This is a really busy area to image, with stars everywhere, from the North American complex itself, as well as in front of and behind the region,” said Rebull. “We refer to the stars that are not associated with the region as contamination. With Spitzer, we can easily sort this contamination out and clearly distinguish between the young stars in the complex and the older ones that are unrelated.”

There are a couple of mysteries about the North American Nebula still to be solved: astronomers think there must be more stars in the “Gulf of Mexico” region that must dominate the nebula and provide the main source of “power.” There is a dark tangle of clouds there that even Spitzers powerful infrared eyes can’t penetrate, but some light appears to be coming from behind that region, in the same way that sunlight creeps out from behind a rain cloud.

The nebula’s distance from Earth is also a mystery. Current estimates put it at about 1,800 light-years from Earth. Spitzer will refine this number by finding more stellar members of the North American complex.

See more info on the JPL website, where you can download full resolution versions of the images seen here, and more views of the North American nebula.

Ambitious Survey Spots Stellar Nurseries

[/caption]

ESO’s VISTA telescope has begun a new survey of the Magellanic Cloud, and this spectacular image of the Tarantula Nebula is a taste of great things to come from this near-infrared scan of the more interesting galaxies in our neighborhood. This panoramic near-infrared view captures the nebula itself in great detail as well as the rich surrounding area of sky. “This view is of one of the most important regions of star formation in the local Universe — the spectacular 30 Doradus star-forming region, also called the Tarantula Nebula,” said the leader of the survey team, Maria-Rosa Cioni from the University of Hertfordshire. “At its core is a large cluster of stars called RMC 136, in which some of the most massive stars known are located.”

VISTA is a new survey telescope at the Paranal Observatory in Chile, and is equipped with a huge camera that detects light in the near-infrared part of the spectrum, revealing a wealth of detail about astronomical objects that gives us insight into the inner workings of astronomical phenomena. Near-infrared light has a longer wavelength than visible light, fortunately, it can pass through much of the dust that would normally obscure the views that our eyes can see. This makes it particularly useful for studying objects such as young stars that are still enshrouded in the gas and dust clouds from which they formed. Another powerful aspect of VISTA is the large area of the sky that its camera can capture in each shot.
The VISTA Magellanic Cloud Survey is one of six huge near-infrared surveys of the southern sky that will take up most of the first five years of operations of VISTA.

This project will scan a vast area — 184 square degrees of the sky (corresponding to almost one thousand times the apparent area of the full Moon) including our neighboring galaxies the Large and Small Magellanic Clouds. The end result will be a detailed study of the star formation history and three-dimensional geometry of the Magellanic system.

“The VISTA images will allow us to extend our studies beyond the inner regions of the Tarantula into the multitude of smaller stellar nurseries nearby, which also harbor a rich population of young and massive stars,” said Chris Evans who is part of the VMC team. “Armed with the new, exquisite infrared images, we will be able to probe the cocoons in which massive stars are still forming today, while also looking at their interaction with older stars in the wider region.”

The wide-field image shows a host of different objects. The bright area above the centre is the Tarantula Nebula itself, with the RMC 136 cluster of massive stars in its core. To the left is the NGC 2100 star cluster. To the right is the tiny remnant of the supernova SN1987A (eso1032). Below the centre are a series of star-forming regions including NGC 2080 — nicknamed the “Ghost Head Nebula” — and the NGC 2083 star cluster.

See more images, zoomable images, and movies of the Tarantula Nebula at the ESO website.

WISE Covers the Heart and Soul of Infrared Astronomy

[/caption]

In about six months’ time, NASA’s WISE mission, the Wide-field Infrared Survey Explorer, has captured almost a million images, covering about three-quarters, or 30,000 square degrees, of the sky. At the 216th American Astronomical Society meeting today, astronomers released a new mosaic of two bubbling clouds in space, known as the Heart and Soul nebulae.

“This image actually has two hearts; one is a Valentine’s Day heart, and the other is a surgical heart that you have in your body,” said Ned Wright of the University of California, Los Angeles who presented the new picture. “This new image demonstrates the power of WISE to capture vast regions. We’re looking north, south, east and west to map the whole sky.”

To make this huge mosaic WISE stared at this region of space which lies about 6,000 light-years away in the constellation Cassiopeia, for 3.5 hours of total exposure time, taking 1,147 images.

Both these nebulae are massive star-making factories, marked by giant bubbles blown into surrounding dust by radiation and winds from the stars. The infrared vision of WISE allows it to see into the cooler and dustier crevices of clouds like these, where gas and dust are just beginning to collect into new stars.

WISE will complete its first map of the sky in July 2010, and then spend the next three months surveying much of the sky a second time, before the solid-hydrogen coolant needed to chill its infrared detectors runs dry. Wright said the first installment of the public WISE catalog will be released in summer 2011.
Wright marveled at how in the span of his career he has gone from observing in just 4 pixels to now observing with WISE in almost 4 million pixels.

“It’s been an amazing progress in IR astronomy, with cameras growing by a factor of a million in power in just a few decades,” he said.

Screen shot from Wright's presentation at the AAS meeting showing how much of the sky WISE has covered. The small green box shows the area of the Heart and Soul nebulae.

Spotting NEO’s

One goal of the WISE mission is to study asteroids throughout our solar system and to find out more about how they vary in size and composition. Infrared helps with this task because it can get better size measurements of the space rocks than visible light.

So far, WISE has observed more than 60,000 asteroids, most of which lie in the main belt, orbiting between Mars and Jupiter. About 11,000 of these objects are newly discovered, and about 50 of them belong to a class of near-Earth objects, which have paths that take them within about 48 million kilometers (30 million miles) of Earth’s orbit.

“As WISE is orbiting the Earth, we are sweeping through the solar system like radar, and building up a map of what the solar system looks like in near infrared, looking for Near Earth Objects,” said astronomer Tommy Grav of Johns Hopkins University.

Grav told Universe Today so far there haven’t been any big surprises in the amount of NEOs the WISE team is finding. “We haven’t done full analysis of all the data WISE has sent back, but we’re finding about what we expected. We’re right in the ballpark of what we expected to find.”

The mission also studies the Trojans, asteroids that run along with Jupiter in its orbit around the sun in two packs — one in front of and one behind the gas giant. It has seen more than 800 of these objects, and by the end of the mission, should have observed about half of all 4,500 known Trojans. The results will address dueling theories about how the outer planets evolved.

“We can basically confirm and fill in the gap between ground based observations and the Spitzer Space Telescope’s observations of the Trojan asteroids,” Grav said.

Grav said WISE is an outstanding observatory. “We’ve basically done in six months what it took over 100 years to do in the optical.”

Sources: NASA, AAS press conference

Young Stars Blast a Hole in Space

[/caption]

There is a black patch of space in NGC 1999, and for years astronomers have thought it was just a dense cloud of gas and dust, blocking light from passing through. But the Herschel infrared space telescope – which has the ability to peer into these dense clouds — has made an unexpected discovery. This black patch is actually a hole that has been blown in the side of the nebula by the jets and winds of gas from the young stellar objects in this region of space. “No-one has ever seen a hole like this,” said Tom Megeath, of the University of Toledo in the USA. “It’s as surprising as knowing you have worms tunneling under your lawn, but finding one morning that they have created a huge, yawning pit.”

Any previous descriptions of NCG 1999 said that the ominous dark cloud in the center was actually a condensation of cold molecular gas and dust so thick and dense that it blocks light. And astronomers had no reason to believe otherwise, until Herschel’s powerful infrared eyes took a look from space.

A Hubble image of NCG 1999 showing the dark patch. Credit: Hubble Heritage Team (STScI) and NASA

When Herschel looked in the direction of this nebula to study nearby young stars, the cloud continued to look black. But, that should not be the case. Herschel’s infrared eyes are designed to see into such clouds. Either the cloud was immensely dense or something was wrong.

Investigating further using ground-based telescopes, astronomers found the same story however they looked: this patch looks black not because it is a dense pocket of gas but because it is truly empty. Something has blown a hole right through the cloud.

Stars are born in dense clouds of dust and gas. Although jets and winds of gas have been seen coming from young stars in the past, it has always been a mystery exactly how a star uses these to blow away its surroundings and emerge from its birth cloud. With Herschel, this may be the first time we can see this process.

The astronomers think that the hole must have been opened when the narrow jets of gas from some of the young stars in the region punctured the sheet of dust and gas that forms NGC 1999. The powerful radiation from a nearby mature star may also have helped to clear the hole. Whatever the precise chain of events, it could be an important glimpse into the way newborn stars disperse their birth clouds.

Source: ESA