Universe Today

February 18, 2010December 24, 2015 by Jean Tate

Roche Limit

Uranus with its moons and rings. Image credit: Hubble

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The Roche limit is named after French astronomy Edouard Roche, who published the first calculation of the theoretical limit, in 1848. The Roche limit is a distance, the minimum distance that a smaller object (e.g. a moon) can exist, as a body held together by its self-gravity, as it orbits a more massive body (e.g. its parent planet); closer in, and the smaller body is ripped to pieces by the tidal forces on it.

Remember how tidal forces come about? Gravity is an inverse-square-law force – twice as far away and the gravitational force is four times as weak, for example – so the gravitational force due to a planet, say, is greater on one of its moon’s near-side (the side facing the planet) than its far-side.

The fine details of whether an object can, in fact, hold up against the tidal force of its massive neighbor depend on more than just the self-gravity of the smaller body. For example, an ordinary star is much more easily ripped to piece by tidal forces – due to a supermassive black hole, say – than a ball of pure diamond (which is held together by the strength of the carbon-carbon bonds, in addition to its self-gravity).

The best known application of Roche’s theoretical work is on the formation of planetary rings: an asteroid or comet which strays within the Roche limit of a planet will disintegrate, and after a few orbits the debris will form a nice ring around the planet (of course, this is not the only way a planetary ring can form; small moons can create rings by being bombarded by micrometeorites, or by outgassing).

Roche also left us with two other terms widely used in astronomy and astrophysics, Roche lobe and Roche sphere; no surprise to learn that they too refer to gravity in systems of two bodies!

More to explore on Roche limits: Saturn (NASA), Roche Limit (University of Oregon), and Tides and Gravitational Locking.

The Roche limit is key to several Universe Today stories, among them Phobos Might Only Have 10 Million Years to Live, Ancient Solar Systems Found Around Dead Stars, and Observing an Evaporating Extrasolar Planet.

Check out these Astronomy Cast episodes for more on Roche limits: Tidal Forces, Tidal Forces Across the Universe, and Stellar Roche Limits.

February 18, 2010December 24, 2015 by Nancy Atkinson

Where In The Universe #92

Here’s this week’s image for the Where In The Universe Challenge, to test your visual knowledge of the cosmos (late again — sorry!) You know what to do: take a look at this image and see if you can determine where in the universe this image is from; give yourself extra points if you can name the instrument responsible for the image. We’ll provide the image today, but won’t reveal the answer until tomorrow. This gives you a chance to mull over the image and provide your answer/guess in the comment section. Please, no links or extensive explanations of what you think this is — give everyone the chance to guess.

UPDATE: The answer has now been posted below.

This is the Stingray Nebula, as seen by Hubble’s Wide Field and Planetary Camera 2 back in 1996.

In this image, the bright central star is in the middle of the green ring of gas. Its companion star is diagonally above it at 10 o’clock. A spur of gas (green) is forming a faint bridge to the companion star due to gravitational attraction.

The nebula is as large as 130 solar systems, but, at its distance of 18,000 light-years, it appears only as big as a dime viewed a mile away. The Stingray is located in the direction of the southern constellation Ara (the Altar constellation).

February 18, 2010December 24, 2015 by Nancy Atkinson

NASA to Invest $75 Million for Suborbital Science Flights

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NASA Deputy Administrator Lori Garver announced today the space agency will fund dozens of science and education payloads to fly on commercial suborbital vehicles. If the 2011 budget proposed by President Obama passes, NASA will commit $75 million in funding over five years for the new Commercial Reusable Suborbital Research program (CRuSR). “For everyone who has dreamed of participating in the grand adventure of spaceflight, this $75 million commitment marks the dawn of a new space age,” said Alan Stern chair of the Commercial Spaceflight Federation’s Suborbital Applications Researchers Group (SARG) and former NASA associate administrator for science. “As the commercial space industry continues to grow, I expect that we will see increasing numbers of payloads and people flying to space.”

Garver made the announcement at the first annual Next-Generation Suborbital Researchers Conference in Boulder, Colorado. Money for payloads means money available for companies like Armadillo Aerospace, Blue Origin, Masten Space Systems, Virgin Galactic, and XCOR Aerospace.

“We are thrilled to see NASA recognizing the enormous potential of new commercial vehicles for science, research, and education,” said Mark Sirangelo, Chairman of the Commercial Spaceflight Federation. “NASA Deputy Administrator Garver’s announcement today means that hundreds of scientists, educators, and students will be able to fly payloads on these new commercial vehicles.”

NASA is proposing to spend $15 million in each of five years from 2011-2015 for the CRuSR program, funds that will both go to universities and other research institutions to build science and education payloads, as well as being used to purchase flights on commercial suborbital vehicles.

“Since this new generation of commercial vehicles are low cost, NASA’s $75 million will open the floodgates for everyone from astronomers to high school classrooms to conduct real science in space,” said STern. “This will be one of the best investments NASA has ever made.”

Source: Commercial Spaceflight Federation

February 18, 2010December 24, 2015 by Nancy Atkinson

Astronomers Find Youngest Exoplanet Yet

Artist's impression of BD+20 1790b, the youngest exoplanet yet discovered. Credit: M. Hernon Obispo

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Overcoming interference from a very active young sun-like star, a group of astronomers were able to find what they determined is the youngest exoplanet yet discovered. BD+20 1790b is 35 million years old (Earth is about 100 times older at 4.5 billion years) and is located about 83 light years away from our planet. Previously, the youngest known exoplanet was about 100 million years old. Studying this planet will help our understanding of planetary evolution.

While this new-found planet is young, it is a whopper, at six times the mass of Jupiter. It orbits a young active star at a distance closer than Mercury orbits the Sun.

Most planet-search surveys tend to target much older stars, with ages in excess of a billion years. Young stars usually have intense magnetic fields that generate solar flares and sunspots, which can mimic the presence of a planetary companion and so can make extremely difficult to disentangle the signals of planets and activity.

BD+201790 is a very active star, and astronomers announced last year that it could possibly have a companion. An international collaboration of astronomers, led by Dr. Maria Cruz Gálvez-Ortiz and Dr. John Barnes were able to “weed out” the data to determine the planet was actually there.

“The planet was detected by searching for very small variations in the velocity of the host star, caused by the gravitational tug of the planet as it orbits – the so-called “Doppler wobble technique,” said Gálvez-Ortiz. “Overcoming the interference caused by the activity was a major challenge for the team, but with enough data from an array of large telescopes the planet’s signature was revealed.”

The team has been observing the star for the last five years at different telescopes, including the Observatorio de Calar Alto (Almería, Spain) and the Observatorio del Roque de los Muchachos (La Palma, Spain).

Source: Alpha Galileo

February 18, 2010December 24, 2015 by Steve Nerlich

Astronomy Without A Telescope – Don’t Make a Meal of It

You should always put out the old dinner set when you have astronomers around. It all starts innocently enough with imagine this wineglass is the Earth rotating on its axis… But then someone decides that large plate is just right to show the orientation of an orbital plane and more wine glasses are brought to bear to test a solution to the three body problem and…

My favorite dinner set demonstration is to use the whole table to represent the galactic plane – ideally with an upturned wide rimmed soup bowl in the middle to mimic the galactic hub. Then you get a plate to represent the solar system’s orbital plane and hold it roughly facing the galactic hub, but at a 63 degree angle from the horizontal. We know the equatorial plane of the Milky Way is tilted 63 degrees from the ecliptic – or vice versa since here we are arbitrarily making the galactic plane (table) the horizontal. This means galactic north is up towards the ceiling – and incidentally a line drawn north up from the galaxy’s centre (i.e. the galactic axis) passes fairly close to Arcturus.

Now for the Earth. Wine glasses make an excellent Earth model since the stem can represent the Earth’s axis of rotation. The glass is at least a bit round and you can see through it for a view of what someone would see from the surface of that glass.

Looking down on the solar system (plate) from its north, which is orientated away from the galactic hub (table), it actually rotates anti-clockwise. So if you hold the glass at the top of the plate – that’s Earth at about September, then move it to the left for December, down to the bottom for March, right side for June and back to September.

So, holding your plate at 63 degrees to the table, now hold the wine glass tilted at 23.5 degrees to the plate. Assuming you left your protractor at home – this will mean the wine glass stem is now almost parallel to the table – since 63 + 23.5 is close to 90 degrees. In other words, the Earth’s axis is almost perpendicular to the galactic axis.

The range of different orientations available to you. The axis of Earth's rotation (represented by the 'celestial equator') is almost perpendicular to the orbital plane of the galaxy.

You should really imagine the plate being embedded within the table, since you will always see some part of the Milky Way at night throughout the year. But, in any case, the wine glass gives a good demonstration of why we southerners get such a splendid view of the galactic hub in Sagittarius. It’s hidden in the daytime around March – but come September about 7pm you get the Milky Way running almost north-south across the sky with Sagittarius almost directly overhead. Arcturus is visible just above the western horizon, being about where the galaxy’s northern axis points (that is, the ceiling above the middle of the table).

And if you look to the north you can see Vega just above the horizon – which is more or less the direction the solar system (plate) is heading in its clockwise orbit around the galaxy (table).

Now, what’s really interesting is if I add the Moon in by just, oh… Er, sorry – that wasn’t new was it?

February 18, 2010March 2, 2016 by Nancy Atkinson

Obama Talks With ISS/Shuttle Crews

Astronauts on the International Space Station took questions Wednesday from President Barack Obama and a group of children. The astronauts eloquently explained the the science and benefits of the ISS, and discussed if artificial gravity could be developed, their thoughts and feelings about being in space, and what they could see from space. “This is really exciting,” said Obama. “We’re investing back here on the ground in a whole array of solar and other renewable energy projects. So to find out you’re doing this up there at the space station is very exciting.”

Obama added, “We wanted to let you know how proud we are of you and how committed we are to continuing human space exploration in the future.”

Let’s hope so.

February 17, 2010December 24, 2015 by Jean Tate

Keck Telescope

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There are two Keck telescopes – Keck I and Keck II; together they make up the W.M. Keck Observatory, though strictly speaking the observatory is a great deal more than just the telescopes (there’s all the instrumentation, especially the interferometer, the staff, support facilities, etc, etc, etc.).

William Myron Keck (1880-1964) established a philanthropic foundation in 1954, to support scientific discoveries and new technologies. One project funded was the first Keck telescope, which was quite revolutionary at the time. Not only was it the largest optical telescope (and it still is) – it’s 10 meters in diameter – but is made up of 36 hexagonal segments, the manufacture of which required several breakthroughs … and all 36 are kept in line by a system of sensors and actuators which adjusts their position twice a second. Keck I saw first light in 1993. Like nearly all modern, large optical telescopes, the Keck telescopes are alt-azimuth. Fun fact: to keep the telescope at an optimal working temperature – no cool-down period during the evening – giant aircons work flat out during the day.

The Keck telescopes are on the summit of Hawaii’s Mauna Kea, where the air is nearly always clear, dry, and not turbulent (the seeing is, routinely, below 1″); an ideal site for not only optical astronomy, but also infrared.

The second Keck telescope – Keck II – saw first light in 1996, but its real day of glory came in 1999, when one of the first adaptive optics (AO) systems was installed on it (the first installed on a large telescope).

2004 saw another first for the Keck telescope – a laser guide star AO system, which gives the Keck telescopes a resolution at least as good as the Hubble Space Telescope’s (in the infrared)!

And in 2005 the two Keck telescopes operated together, as an interferometer; yet another first.

To learn more, I suggest that you start with the official W.M. Keck Observatory website! Revolution in Telescope Design Debuts at Keck After Birth Here is a 1992 Lawrence Berkeley Lab article which captures some the excitement of those early days; and The Keck Telescopes viewed from the North puts the Keck telescopes in the Mauna Kea context.

Universe Today has covered the Keck telescopes, many times, in many different ways; for example, Keck Uses Adaptive Optics for the First Time, Binary Icy Asteroid in Jupiter’s Orbit, and New Technique Finds Farthest Supernovae.

Astronomy Cast has a couple of episodes on the Keck telescopes; check them out! The Rise of the Supertelescopes, and Adaptive Optics.

February 17, 2010December 24, 2015 by Jean Tate

Electron Volt

Fermi mapped GeV-gamma-ray emission regions (magenta) in the W44 supernova remnant. The features clearly align with filaments detectable in other wavelengths. This composite merges X-ray data (blue) from the Germany/U.S./UK ROSAT mission, infrared (red) from NASA’s Spitzer Space Telescope, and radio (orange) from the Very Large Array near Socorro, N.M. Credit: NASA/DOE/Fermi LAT Collaboration, NASA/ROSAT, NASA/JPL-Caltech, and NRAO/AUI

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From the name, electron volt, you might guess that this has something to do with electricity. Well, you’d be right, it does … but did you know that the electron volt is actually a unit of energy, like the erg or joule?

The symbol for the electron volt is eV – lower case e, upper case V. Like the meter, and parsec, the electron volt can have a prefix, so lots of electron volts can be written easily, so there’s a kilo-electron volt (keV, one thousand eV), mega-electron volt (MeV, one million eV), giga-electron volt (GeV, one thousand million eV), and so on.

About the energy the electron volt represents: if you accelerate an isolated electron through an electric potential difference of one volt, it will gain one electron volt of kinetic energy. Now a volt is a joule per coulomb, so an electron volt is one electric charge times one, or approx 1.6 x 10^-19 joules (J).

Astronomers use electron volts to measure the energy of electromagnetic radiation, or photons, in the x-ray and gamma-ray wavebands of the electromagnetic spectrum, and also use electron volts to describe the difference in atomic or molecular energy states which give rise to ultraviolet, visual, or infrared lines, or limits. So, for example, the Lyman limit – which corresponds to the energy to just ionize an atom of hydrogen – is both 91.2 nm and 13.6 eV.

Now particle physicists use the electron volt, as a unit of energy too; however, confusingly, they also use it as a unit of mass! They do this by using the famous E = mc² equation, so 1 eV – the unit of mass – is equal to 1 eV (the unit of energy) divided by c² (c is the speed of light). So, for example, the mass of the proton is 0.938 GeV/c², which makes the GeV/c² a very convenient unit (= 1.783 x 10^-27 kg). By convention, the c² is usually dropped, and masses quoted in GeV.

Oh, and in some branches of physics, the eV is also a unit of temperature!

Would you like to read more on the electron volt? Try Energetic Particles (NASA), and How Big is an Electron Volt? (Fermilab).

Universe Today has many stories in which the electron volt features; here is a sample: Is a Nearby Object in Space Beaming Cosmic Rays at Earth?, Gamma-ray Afterglow reveals Pre-Historic Particle Accelerator, and Gamma Ray Bursts May Propel Fast Moving Particles.

The Astronomy Cast episode Gamma Ray Astronomy is a good example of electron volts in action.

Sources:
Wikipedia
NASA Science
GSU Hyperphysics

February 17, 2010December 24, 2015 by Jerry Coffey

Atom Diagram

[/caption]The image on the left is a basic atom diagram. This one shows the protons, neutrons, and electrons of a carbon atom. Each is in a group of six. That makes the atom very stable. There have been many atomic models over the years, but this type of model is now widely considered a sound basic version. Atomic diagrams were developed to explain the interaction of the elements of the Earth and space long before atoms could be observed. Nowadays, scientists can see particles that are smaller than an atom. These sub-atomic particles are the basis of particle physics.

Scientists have used atomic diagrams to explain the workings of the world for centuries. The ancient Greeks and, before them, the Chinese and Babylonians believed that there were forces that could not be seen that allowed certain metals to be combined and worked to man’s advantage. They did not know it, but that was simply heated metals exchanging subatomic particles to become a new metal.

Basic chemistry explains the atom best. It states that the fundamental building block of matter is the atom. An atom consists of three main parts: protons, neutrons, and electrons. Protons have a positive electrical charge. Neutrons have no electrical charge. Electrons have a negative electrical charge. Protons and neutrons are found together in what is called the nucleus of the atom. Electrons circle around nucleus. Chemical reactions involve interactions between the electrons of one atom and the electrons of another atom. Atoms which have different amounts of electrons and protons have a positive or negative electrical charge and are called ions. When atoms bond together, they can make larger building blocks of matter called molecules. If science did not have the atom modeled out, it would never have understood this exchange of electrons and we could still be stuck in the Dark Ages.

Earlier, I mentioned that there had been many atom models developed. Some of them are the Bohr model, the cubic model, the plum pudding model, the Saturnian model, and the Rutherford model.
Each of these models improved on the other and propelled science closer to a perfect atomic model. The Bohr and Rutherford models were developed for quantum mechanics and used for astronomical applications. As a matter of fact, an improvement on the Bohr model, called the Bohr-Summerfield model, is responsible for some of the many things we now know about quantum mechanics.

The atom diagram is under constant revision as science uncovers more information about sub-atomic particles. Follow this link to get information about the Bohr model and its enhancements. Here on Universe Today we have two great articles: one about the proton and the other about electrons. Astronomy Cast offers a good episode about matter from stars.

Sources:
Wikipedia
Chemistry Help

February 17, 2010December 24, 2015 by Jerry Coffey

Atom Definition

[/caption]The atom definition is: A unit of matter, the smallest unit of an element, having all the characteristics of that element and consisting of a dense, central, positively charged nucleus surrounded by a system of electrons. The entire structure has an approximate diameter of 10^-8 centimeters and characteristically remains undivided in chemical reactions except for limited removal, transfer, or exchange of certain electrons. Essentially, it is the smallest possible part of an element that still remains the element.

Under normal circumstances an atom can be broken down into any smaller particles, but we humans, have devised ways to break the atom apart. That is the entire basis of the atom bomb, particle colliders, and quarks. It takes high speed, high energy smashing of particles to break an atom. A particle collider does that and helps us understand some of the theories in particle physics. The results of an atom bomb are widely known. Quarks are extremely small particles that do not exist alone. They must group to form the protons, electron, and neutrons normally found in a single atom of an element. They have only been found as a result of a particle collider and in theory.

An atom itself is made up of three tiny kinds of particles called subatomic particles: protons, neutrons, and electrons. The protons and the neutrons make up the center of the atom called the nucleus and the electrons fly around above the nucleus in a small cloud. The electrons carry a negative charge and the protons carry a positive charge. In a normal (neutral) atom the number of protons and the number of electrons are equal. Often, but not always, the number of neutrons is the same, too. The opposing forces(negative and positive) attract and repel each other in the right way so as to keep the atom together. The universe could be looked at as one large atom. Everything in space attracts and repels just right so as to keep the whole together.

One type of theoretical ion propulsion spacecraft would have to take advantage of this atomic attraction and repulsion to operate. It takes advantage of magnetism and electricity to push a ship through space. Electricity, generated by the ship’s solar panels, gives a positive electrical charge to atoms inside the chamber. They are pulled by magnetism towards the back of the ship and then pushed by magnetic repulsion out of the ship. This steady stream of atoms going out of the spacecraft gives it the thrust it needs to go forward through space. NASA has tested other types of ion propulsion and found them lacking.

Here is another atom definition. Here on Universe Today we have a great article about atoms. Astronomy Cast has a good question and answer episode about interstellar travel, including a NASA link about ion propulsion.

Source:
Wikipedia