Hopefully we are all aware of the fact that ultraviolet rays from the Sun are bad for our skin. The reason they are hazardous is because of the high energy that that they possess, which allows them to penetrate our skin and damage the cells internally. UV is a small part of our Sun’s emissions but UV radiation is a major component of the energy emitted by very hot, massive stars, as can be seen in the image below from NASA’s Galex (Galaxy Evolution Explorer) satellite.
Andromeda Galaxy in UV - Image courtesy of NASA
These stars that line the arms of the Andromeda galaxy are the result of dust and gas that form the structure of the arms and consequently, the birthing place of new stars. Blue giants have very high surface temperatures ranging from 10,000 to more than 40,000 degrees Kelvin. The more massive the star, the hotter it is and the more it will radiate in the ultraviolet. But, running hot and massive comes with a cost. These blue giants will burn out in supernovae in a few tens of million of years. (A very short time – astronomically speaking!) Compare this with our Sun, which has a surface temperature of about 6000 degrees Kelvin and will be around for at least 10 billion years.
Below you can see Andromeda in a Hubble image in the optical spectrum fading to the ultraviolet image from Galex. It’s easy to see that these high-powered stars reside in the dusty arms of the galaxy. In a few million years the Milky Way Galaxy will have a ring-side seat to view these blue giants as they spectacularly end their lives!
A smudge in the night sky can contain many wonders!
Ground-based, wide-field view of NGC 2366 from Digital Sky Survey 2 - Image courtesy of NASA
The blue streak in the above image is the dwarf galaxy NGC 2366. It is about 10 million lightyears distant and located in the constellation Camelopardalis (the Giraffe), which is visible in the northern hemisphere. Barely visible to the bottom right of the blue smudge is a bright spot, which is an active star-forming nebula, NGC 2363 contained within the dwarf galaxy. In the image below you can see the nebula shining from the light of the hot blue stars that are forming in the upper right part of the galaxy.
Hubble view of NGC 2366 - Image courtesy of the NASA/ESA Hubble Space Telescope
Zooming in on the nebula in another Hubble image below, one can see the collection of bright stars embedded in the nebula. Of particular note is the very bright star that appears at the tip of the “hook” of the nebula. This massive star is known as a Luminous Blue Variable (LBV), which is about 30 to 60 times as massive as the Sun. This is a very rare type of variable and very unstable. The image captured the star during an erupting phase. Another, more famous star of this type is the giant, Eta Carinae, which is anticipated to turn into a supernova in the near future (astronomically speaking).
NGC 2363 - Star forming nebula in the dwarf galaxy NGC 2366 - Image courtesy of NASA
When you look closely at the image of NGC 2366 you will see many “nebulous” regions within it. They are actually very distant galaxies that are visible through the veil of the dwarf galaxy. I’ve highlighted some of the more prominent galaxies that can be found in the image below.
Galaxies beyond NGC 2366 - Base Image courtesy of NASA/ESA Hubble Space Telescope
Here is a composite of some of the major galaxies hiding behind this dwarf galaxy.
Galaxies behind the dwarf galaxy NGC 2366
NGC 2366 is just another example of what wonders are hidden within the smallest parts of the night sky and what amazing things are awaiting discovery.
In the first blog on finding exoplanets I discussed the transit technique that is used to find planets by the light they block as they pass in between their star and the Earth. That gives information on the size of the planet, its orbit as well as information on the atmosphere of planet if it has one. But, there is a critical piece of information that is not supplied by the transit technique and that is the mass of the planet. Finding the mass of the exoplanet is done by measuring its radial velocity – its velocity as it moves toward and away from us as the planet or planets pull on it while orbiting the star.
Theoretically, one could measure a star’s motion relative to stars more distant as a planet tugs it one way or another, but in practice it is extremely difficult to measure this tiny displacement. This is the branch of astronomy known as astrometry. This technique has has not had much success due to limitations in the optics used in the telescopes and atmospheric turbulence. The more distant the star of interest is, the more imprecise the measurements become.
The technique that has been very successful utilizes the Doppler shift or the change in frequency of star’s light as it is pulled back and forth by its planets. Just like the sound of a train whistle increases in frequency or pitch as it moves toward you, and decreases as it moves away, the light from the star increases in frequency (gets bluer or is blueshifted) when the star is pulled toward us and decreases in frequency (gets redder or is redshifted) as it is pulled away from us.
To use this technique the light from the star is broken into its constituent parts by using a spectrograph and the shift of the spectrum can be measured with great precision as the star moves, allowing astronomers to calculate the minimum mass of the planet(s) that orbit the star.
The shift of a star's spectrum as it is pulled by an orbiting planet
In the image above, one can see the star moving around a center of mass determined by the mass of the star and the planets orbiting it. The spectrum shows black lines which are created by elements in the star’s atmosphere that characteristically absorb electromagnetic energy—light—at different frequencies. These lines are used to determine the composition of the star’s atmosphere, but it is the displacement of these lines that astronomers measure to determine the radial velocity and then the minimummass of the planet. The last image in the graphic shows the absorption lines as they shift toward the red and blue ends of the spectrum.
Note the emphasis on the minimum mass. This is the mass calculated by the component of the star’s velocity that is directly toward/away from us — its radial velocity. If the orbital plane of the planet is not directly in our line of sight (i.e. its orbit is inclined at some angle) then we are not seeing the total velocity of the star due to the planet, only a component of it (Remember your vectors!). If we don’t know the orbital inclination of the exoplanet to its star, then the mass we calculate based on the radial velocity we measure is a minimum mass and could be higher. If it turns out that the planet is orbiting in a plane directly in our line of sight, then the mass measured would be the actual mass.
HARPS can resolve radial velocities to 1 meter per second. That translates to a star moving toward or away from us at a velocity of 3.6 km/hour, or 2.2 mph—that’s average walking speed for humans! To get an appreciation for these numbers, consider if we were looking at our Sun from a distant star using the HARPS spectrograph. We would easily be able to detect Jupiter’s influence on the Sun, which provides a radial velocity of 12.7 m/s. Earth, however, would not be detectable because it only disturbs the Sun on the order of .1 m/s. But, it is not just the size of the planet that determines how much it will affect the radial velocity of the star but also its distance from the star.
Having a value for the mass of an exoplanet allows astronomers to determine the planet’s density and determine its probable composition. Having an educated guess at the planet’s make-up and knowing its distance from its star, and therefore its likely surface temperature, one can then speculate as to the state of water on the planet if present and the likelihood of life as we know it.
More and more evidence is surfacing that keeps increasing the number of potential planets in the average galaxy. The higher the number of planets, the better the odds of finding a habitat that is conducive to life. And, if we extend our theorizing to the number of moons that may orbit these planets, the number of potentiality habitable planets is…well…astronomical!
Extraterrestrial civilization on a moon of a gas giant in a distant solar system. -RC Davison
With Kepler increasing the total number of potential planets discovered almost daily, (as of 3/10/2012 the total is at 2321 with 61 planets confirmed) it is becoming easier to take this exciting news for granted. There is a lot more going on behind the scenes to these discoveries than just pointing a telescope at the stars and waiting for the planets to go by. Kepler uses a technique called the transit method to identify potential planets, but there are other ways to find planets, which I will discuss in a future post.
The transit method requires that the planets revolve around their stars in a plane that is within our line of sight, so from our perspective the planet blocks the light coming to us from its star. In concept this is pretty straight forward and simple. But, as they say, the devil is in the details.
If you click on the image above you will see a simulation provided by the Kepler site of a planet transiting the star it orbits. What’s interesting to note is the gradual slope of the curve as the planet first begins to cross the star or ingress and is repeated on the other side when the planet egresses the star. Also, as the planet transits the face of the star the light curve is not flat but curved due to limb darkening effects. The curve is not smooth, which indicates the variability in the brightness across the star’s surface. Note that in most cases the amount of light blocked by the planet is only on the order of 1% – 2%.
Consider this. As you watch the light dim from the star are you really seeing a planet passing in front of it or are you seeing the star itself dim because it is a variable star or has a large starspot (sunspot) on its surface that just came into view or some other phenomena is affecting the light you are seeing?
Maybe the dimming is due to the fact that this is not one star but two in a binary system – two stars orbiting each other in a plane that lies along our line of sight. What you perceive as dimming due to a planet could really be one star eclipsing the other. You would get the brightest image when they are not eclipsing, the dimmest when one is behind the other. These are known as eclipsing binaries. (Note that Kepler has discovered 2165 eclipsing binary stars as of this blog post) And, what if it’s a trinary system – three stars orbiting a common center of mass? Throw in a few planets and try to imagine the light curve for that system!
The dimming has to be periodic and repeatable to increase confidence that there really is something out there orbiting the star and not just an intervening asteroid or comet that happened to pass through your field of view. Kepler requires 3 to 4 events to record a potential exoplanet. The first planets Kepler discovered had orbital periods of several days, which allowed astronomers to gather a set of data in a very short time. These planets are very close to their star and are extremely hot.
Kepler has been observing for 3 years now, so it will be finishing up data sets on planets that are orbiting further from their star with orbital periods of a year or so. The longer Kepler looks, the more planets it will unveil.
Through various techniques like spectroscopic analysis one can determine if the star is part of an eclipsing binary pair. Through other observations one can determine if the star is a variable star and if the dimming doesn’t reappear, then it may have been a starspot or other transient phenomena. If the dimming repeats and you collect a set of light curves that show how much light is blocked by the object you can then begin to determine some interesting properties about this object, like how big it is, what its orbital period is and distance from its parent star. But, these numbers don’t come without some hard work.
It’s easy to get a relative size of the planet to its star by how much light it blocks when the planet transits the face of the star. But, one needs to take into account a number of physical phenomena that will affect the data that is collected. One of these is limb darkening – which is the effect that the star is not as bright at its edges (limbs) as it is at the center. This is due to the fact that one is not looking as deeply into the star at its edges as at its center. This means that the planet will block a greater percentage of light as it traverses the center of the star than at the edge.
Where the planet crosses the star will affect the shape and size of the light curve. Crossing directly over the equator of the star would produce the broadest, most shallow curve while crossing the star at higher latitudes would produce a narrower, deeper curve. This is a reflection of the tilt of the planet’s orbit relative to Earth. These will affect the calculations of how big the exoplanet is and how large its orbit is and must be taken into account.
Transit Light Curves - Image Courtesy of NASA/JPL
Starspots can also skew the data if they occur as the planet transits the face of the star. This is because they are dark and they will add to the amount of light perceived to be blocked by the planet, giving the impression that the planet is bigger than it really is.
An advantage of the transit method is that it allows astronomers to determine if the planet has an atmosphere. Using a spectrometer it is possible to determine the constituents of the planet’s atmosphere as the star’s light passes through the planet’s atmosphere as the planet passes over the edge of the star at the beginning and end of the transit.
The transit method provides information on how big the planet is, once the size of its parent star is known, which is a challenge in its own right. Once the planet’s size is determined and coupled with mass data gleaned from another technique—radial velocity measurement—the density of the planet can be calculated. When the density is known, approximations can begin to be made about the composition of the planet. Is it gaseous, rocky, or somewhere in between? This information, along with the knowledge of how close to its star it orbits, which determines the temperature of the planet, will dictate what state water might exist if present.
The science of astronomy is an amazing example of how inventive and ingenious man can be. We have harvested all we know about our Universe from just the light that comes to us through the vacuum of space.
Take a huge volume of hydrogen gas mixed with some helium and other trace elements from the last star that went supernova in the cosmic neighborhood, wait for it to coalesce and blaze into an average star like our Sun, sit back and relax for the next 10 billion or so years and you will eventually get something that looks like this:
Helix Nebula Taken by the Palomar Observatory
Well, in 1952 that was the best image we could get of the Helix Nebula. It was taken with the 200 inch Hale telescope at the Palomar Observatory in California. This black and white image only gives us a glimpse of this planetary nebula – the remains of a Sun-like star’s final death-throws.
Today, the same nebula looks like this:
Helix Nebula by the Hubble Space Telescope
Please note that this striking difference is not evidence of the changes the nebula has gone through but the revolution we have had in astronomy, especially with terrestrial based telescopes with adaptive optics to compensate for our dynamic atmosphere.
This optical image of the Helix Nebula was taken in May of 2003 was taken by the Hubble Space Telescope and composited with images taken with a smaller telescope at the Kitt Peak National Observatory in Arizona. The compositing was done because of the large area the nebula covers—almost half the diameter of the full Moon—and Hubble’s small field of view. In this optical image the red color indicates oxygen while the blue corresponds to nitrogen and hydrogen.
Looking deeper into the interior of the nebula one can see comet-like structures shown below.
Close-up view of the Helix Nebula by the Hubble Space telescope
To get a sense of size, these bulbous, comet-like shapes are on the order of the size of our Solar System. They have been sculpted out of the dust and gas by the high energy solar wind coming off the white dwarf star located at the center of the nebula. The material was blown off from the original star when it ballooned into a red giant several times as it aged and consumed its fuel—hydrogen.
The Helix Nebula is one of the closest at a distance of about 650 light-years from Earth, and it is about three to six light-years across. It can be found in the constellation of Aquarius. The Helix also goes by its catalog number NGC 7293.
Originally called the Helix because it was thought that we were viewing the nebula along its length. More recent research seems to indicate that the nebula instead of tube-like is more like a bubble with a ring of debris. This can be more easily seen in the video below where a 3D projection of the nebula has been simulated. This may be indicative of a binary system.
When we venture into the infrared part of the spectrum, we can see structures that are hidden by the dust and gas that absorb the visible wavelengths of light. The Spitzer Space telescope has presented several views of the Helix Nebula taken in 2007.
Helix Nebula in infrared by the Spitzer Telescope
The region of the white dwarf can be seen in the image below as a bright white dot in the center of the red zone. Note that this is not the star, which is about the size of the Earth, but the surrounding cloud of dust and debris that remains around the star. If you look closely you can see a circular zone of dust surrounding the white core, which is a high concentration of dust and debris akin to the Oort cloud that surrounds our star, which harbors a tremendous number of comets, asteroids, planetoids and debris from the early stages of the Solar System.
Helix Nebula by the Spitzer Space Telescope
The image below shows a composite between the visual and infrared. Hubble and Spitzer images have been combined to show even more detail. Higher energies exist nearer the center, indicated in blue to lower energy – yellow to the cooler reds at the edges.
Composite of visual and infrared image of the Helix Nebula by the Hubble and Spitzer Space Telescopes
Still looking at the nebula in the infrared we get this amazing image on the left from the 4.1 meter VISTA (Visible and Infrared Survey Telescope for Astronomy) at the ESO’s Paranal Observatory in Chile. Just as in the Spitzer images above we see much more of the structure of the nebula because we are looking at the longer wavelengths in the infrared.
Helix Nebula in infrared by the European Southern Observatory
It is interesting to note that all the dust and gas that you see in the image, covering 6 light-years at its widest is star-stuff, debris from the star itself. It’s easy to see how stars, the factories of all the elements that we know, can distribute these elements across the cosmos. Under a more benign death such as this, material is being scattered across a huge area. Imagine the consequences of a supernova!
In about 5 billion years our star will begin to form its own planetary nebula. As beautiful as these nebulae are it is important to understand that they are transitory. They will spread out and disperse over time and disappear. In about 50,000 years the Helix will be gone. Enjoy it while it lasts!
The center of our galaxy is a very busy place, and it has been under close scrutiny by astronomers since 1992. A team of astronomers have been watching our galactic core, peering through the veil of dust that shrouds the core using infrared eyes via the European Southern Observatory’s New Technology Telescope and the Very Large Telescope. What they’ve seen shows a group of stars doing a mesmerizing dance around an object that we can not see, but has a definite influence on their orbits. The following video from ESO gives a great introduction to this amazing phenomena.
A black hole? Like the saying goes – “If it walks like a duck, quacks like a duck and looks like a duck, it’s probably a duck!” The motion of these stars and other information gathered over the years indicates that there should be an object at the center of our galaxy with a mass equivalent to about 4 million Suns. Based on the latest theories, this should be a black hole.
Recently, Dr. Reinhard Genzel of the Max-Planck Institute and his team have discovered a cloud of dust and gas that appears to be heading for a close encounter with this object dominating our galactic center. The dust cloud, which is about three times as massive as the Earth, has doubled its speed over the last seven years, not something an object can do unless it has its own propulsion system or it is in a substantial gravity well – i.e. in the grip of a black hole. Astronomers predict that the cloud will pass by the black hole at a distance of about 40 billion kilometers – equivalent to about ten times the distance between the Sun and Neptune. The following video shows the time-lapse motion of the cloud as well as stars at the core.
Although the cloud is being ravaged by the black hole now, in 2013 it should be at its closest to the black hole and be ripped apart. This encounter should be indicated by a brightening of this region, especially in X-ray portion of the spectrum, as the dust and gas particles are heated to millions of degrees as they collide with each other while spiraling down to the event horizon of the black hole and beyond.
The following video shows a simulation of the cloud in red/yellow as it approaches the black hole. The time frame is from the year 2000 to 2043.
This will be a great opportunity to see a black hole feeding, as well as testing Einstein’s General Theory of Relativity as it applies to black holes. We can look forward to some celestial fireworks in 2013!
Known unofficially as the “Ghost Nebula” or “Ira’s Ghost”, this vast cloud of interstellar dust harbors an incubator for new stars. Discovered in 1983 by the IRAS satellite (InfraRed Astronomical Satellite), it is officially known as IRAS 05437+2502 (Ira’s Ghost sounds a lot spookier!). This image was taken in visible light by the Hubble Space telescope and released in June 2010.
Located in the constellation of Taurus, the nebula covers about 1/18th the size of the full Moon. The bright inverted “V” seen in the upper left of the nebula is a rather perplexing structure. One theory is that it may have been formed by a large star that was ejected from the nebula at an extremely high speed. For more information about Ira’s Ghost, check out the Hubble site.
Enjoy your Halloween, and be very glad that Ira’s Ghost is far, far away!
“Space, the final frontier.” Simple words spoken by Captain Kirk, of the starship Enterprise, but ones that create a sense of excitement and wonder.
But, is “space” our final frontier? With the billions upon billions of galaxies out there, containing an uncountable number of stars and an unimaginable number of planets, is it our last frontier?
Hubble Ultra Deep Field - Image Courtesy of NASA
There is something about space…so vast, so enigmatic, so alluring. I have long gazed at the stars and felt that there is so much out there to discover and learn about—things that would just boggle our minds. And, we already see it today with the amazing image from the space telescopes like Hubble and Spitzer and terrestrial observatories like Keck and the European Southern Observatory’s Very Large Telescope. It may truly be the final frontier. But, for us to be out among the stars, and, if you can imagine it, out among the galaxies, we will have to conquer hurdles and challenges that will include understanding how our Universe works. More importantly, we need to understand how we work, as biological entities, as well as cultural and societal beings, because we will never have the strength and dedication to reach for the stars if we can not respect, have consideration for, and cooperate with one another.
Thinking about it a bit more, maybe that is our final frontier. Not “space” as Gene Roddenberry so simply stated way back in 1966 when Star Trek first beamed into our homes on our televisions. Maybe he was really speaking of a frontier more subtle, more challenging than traveling to the stars. Maybe that frontier is simply people working together—united—where our challenges are no longer with each other but come from beyond the humble abode we call Earth.
I’m afraid that once we do step out into the cosmos, beyond the comfort of our blue planet and yellow sun, and travel to these other stars, solar systems and planets to study them up close, each will offer more unknowns that will push the boundary of our final frontier. Undoubtedly there will be more things discovered that will have us scratching our heads and wondering just how does that work. That bewilderment may very well come more from the biology we find rather than the new physics we might discover. And, that doesn’t even address the issues of us trying to comprehend alien cultures and societies that have absolutely no parallel to what we’ve experienced on Earth!
So, where does the boundary exist to define the final frontier? Unfortunately, I think it will be a boundary we will approach asymptotically—always getting closer but never really reaching it—and I can’t wait! There’s so much to discover!
Hopefully, some food for thought; so think about it, talk about it, comment on it—I’d be happy to hear your views on our final frontier.
Some said it wouldn’t be possible, but Kepler has revealed a binary star system that has a planet (Kepler-16b) orbiting around it. To some this is reminiscent of Tatooine, Luke Skywalker’s home planet in the “Star Wars” saga.
Artist's concept of planet orbiting the binary star system - Kepler-16b Image courtesy of NASA
This planet, which is about the size of Saturn, cold, possibly gaseous and rocky and orbits around the pair of stars in 229 days. It also lies outside the habitable zone of these stars, which is the zone around a star that water would exit in a liquid state. The two stars are smaller than the Sun, being about 69% and 20% the mass of our star.
Here’s a nice video showing the dynamics of this unique system and provides some great background information.
To say that such a planetary system could not exist was so very short sighted. We have just begun to uncover the wonders of this Universe we live in. I can only imagine what other wonders are out there that someone has stated emphatically would be impossible. The possibilities are endless!
Welcome to the first posting at ORBITAL MANEUVERS new blog site!
I will be moving the posts from the old site shortly, but until then the original site is still available. This move will allow more flexibility in the blog posts. Now on to the good stuff!
In the novel, ORBITAL MANEUVERS, the asteroid that impacts Earth escaped detection for of a number of reasons, but one of the main reasons is that it was composed of a material that was blacker than black — it reflected almost no light. How black is that?
The scientific term used to quantify this blackness is albedo. It is simply the ratio of the amount of incident light on an object to the amount of light reflected back. For the Moon, it is on average about 12%. Think about that the next night you are out and the full moon is shining above. Only 12% of the light from the Sun reflects off the surface of the Moon. Imagine what it would be like if it was 50% or higher! Also, for another twist on this, consider that the average albedo of a paved, blacktop road surface is about 10%. So, that bright orb in the night sky really isn’t any brighter than the road you may be driving or walking on!
Now let’s take a look at this new planet that was discovered by Kepler, TrES-2b, about 750 light-years distant in the constellation of Draco the Dragon. Although this planet is extremely hot, about 1,800 degrees Fahrenheit (980 degrees Celsius, it is extremely dark, with an albedo of slightly less than 1%. Coal has an albedo of about 1%, which is a something most people can relate to and it’s pretty dark, but we’ve found asteroids in our Solar System that have an albedo of about .6%. On the other end of the spectrum we have Saturn’s icy moon Enceladus, which has an albedo of 99%.
Artist's impression of TrES-2b - Image courtesy of David A. Aguilar (CfA) Harvard Smithsonian Center for Astrophysics
So, it’s not beyond the realm of possibility that the asteroid that impacts Earth in the novel is so dark that the surveillance systems in place at the time could have missed it. It’s nice to know that we are more active today as far as monitoring asteroids in the Solar System than we were ten years ago when the novel was started.
What is TrES-2b made of? We don’t know. Add that to the list of things we need to learn about in this vast Universe we live in. The wonders never cease!