Universe Today

November 16, 2009April 26, 2016 by Nicholos Wethington

NASA to Fund Primate Radiation Research

Monkeys have made contributions to spaceflight before, and NASA plans to start using them again to test the effects of radiation exposure on their performance of various tasks. With renewed efforts to send humans to the Moon and Mars – which exposes them to radiation from the Sun and galactic cosmic rays – NASA wants a better idea of exactly what the effects of this radiation will be on the cognitive performance of astronauts. A research proposal on the effects of radiation in primates is just one of twelve studies that NASA has chosen to fund through its Human Research Program grants for space radiobiology research.

The study, proposed by Jack Bergman, who is an Associate Professor of Psychobiology at Harvard Medical School’s McLean Hospital in Belmont, Massachusetts, will test how the exposure to radiation of 18-28 rhesus monkeys will effect their performance at trained tasks. They will be subjected to a single dose of radiation that is equivalent to what an astronaut would encounter on a three-year mission to Mars. After the exposure, the monkeys will be monitored as to how they perform tasks which they have been trained to do on a computer touch screen.

“The beauty of this is that we can assess at different time points after exposure, so not only do we get a sense of rather immediate effects, but then we can look again at longer time points. That kind of information just hasn’t been available,” Bergman told Discovery News.

The aim of such research is to see exactly how radiation exposure will alter the performance of astronauts on a long-term mission to Mars. Radiation exposure has been shown in mice and rats to effect their overall cognitive performance, but little is known as to what effects will occur in humans at such radiation levels. This is why the study will be done on primates, which are much closer in biological makeup to humans.

The monkeys will not be killed after the experiment ends, and will remain at the McLean hospital for care during the remainder of their lives.

NASA has enlisted rhesus monkeys before, in the 1940s into the 1960s, to study the effects of launch and re-entry into space. A number of rhesus and squirrel monkeys were launched into space, and many did not survive the re-entry. These experiments paved the way for human spaceflight, and gave NASA information as to what was needed to protect the astronauts from the inherent danger of going into space.

The decision by NASA to fund this experiment has of course raised concerns about the ethical nature of such experiments. The Physicians Committee for Responsible Medicine sent an appeal to NASA administrator Charles Bolden, charging that the experiments are in violation of the Sundowner Report, guidelines set by NASA regarding the ethical treatment of animals used in research.

When the experiments are to begin is still unclear, as the research proposal is still pending approval by the Brookhaven National Laboratory in Upton, New York, where the actual irradiation research will take place.

Source: Discovery News, New Scientist

November 16, 2009December 29, 2015 by Nancy Atkinson

Carnival of Space #129

This week’s Carnival of Space is hosted over at Tiny Mantras.

Click here to read the Carnival of Space #129.

And if you’re interested in looking back, here’s an archive to all the past Carnivals of Space. If you’ve got a space-related blog, you should really join the carnival. Just email an entry to [email protected], and the next host will link to it. It will help get awareness out there about your writing, help you meet others in the space community – and community is what blogging is all about. And if you really want to help out, let Fraser know if you can be a host, and he’ll schedule you into the calendar.

Finally, if you run a space-related blog, please post a link to the Carnival of Space. Help us get the word out.

November 16, 2009December 24, 2015 by Ken Kremer

Tweeters and Atlantis Ready for Launch

(Editor’s Note: Ken Kremer is in Florida for Universe Today covering the upcoming Atlantis launch attempt.)
Space shuttle Atlantis is all fueled up and ready for launch. Liftoff time is slated for 2:28 PM EST Monday. The weather forecast has degraded somewhat to 70 percent acceptable from the prior 90 percent forecast. The only concern is the possibility of low cloud ceilings this afternoon. Skies are overcast here at the KSC press center. All the emergency landing sites are “Green”. The launch team is not working any issues at this time. Among those on site at Kennedy Space Center are about 100 Twitter devotees, who are part of a special NASA “Tweet Up.” They’ve been able to tour different facilities and will be on hand for the launch attempt today.

Close up of Space Shuttle Atlantis and crew walk out arm and platform at 195 ft level of pad 39 A. Close out crew assists crew into their seats. Thereafter the orbiter hatch is closed for the 11 day mission to the ISS. The arm swings away a few minutes prior to launch. Credit: Ken Kremer

The “tanking” procedure began with a 10 minute chill down of the pipes at pad 39 A. Valves leading to the bottom of the 154 foot tall External Tank (ET) were cracked open to begin the roughly 3 hour fueling process of cryogenic propellants. Approximately 535,000 gallons of supercold liquid oxygen (LOX, minus 298 deg F) and liquid hydrogen (LH2, minus 423 deg F ) are loaded from storage tanks around the pad to the shuttles mobile launch platform and is nearly complete as of 7 AM. Thereafter the LOX (145,000 gallons) and LH2 (390,000 gallons) are replenished as needed.

The final inspection team will then proceed to pad 39 A to carefully inspect the ET for any signs of ice build-up which could fall off the ET during ascent and potentially damage the shuttle. The cryogenic propellants fuel the orbiters three main engines (SSME’s) during liftoff and ascent for the 8 and a half minute climb to orbit.
This is the 129th Space Shuttle flight, the 31st flight of Atlantis and the last flight of 2009. Only 5 flights remain after STS 129.

The countdown clock began ticking at T minus 6 hours with the start of fueling.

Media from around the globe have descended on the Kennedy Space Center press site to report on STS 129. I met journalists from many countries including India, Australia, Japan, Korea, Slovenia, Poland, Netherlands, Germany, Turkey, United States and more. RSS rollback has just commenced as we stand at the perimeter security fence surrounding Pad 39 A. Credit: Ken Kremer

On Sunday, I watched from a mere few hundred meters away as NASA technicians retracted back the Rotating Service Structure (RSS) at Launch Pad 39 A to unveil a gleaming white Space Shuttle Atlantis for her heavenly trek to the International Space Station (ISS). Media numbering perhaps a hundred from around the globe, including many from across Asia, were on hand to witness the event which began at 5:30 PM EST as the sun was setting.

The global nature of the news coverage augers well for interest in the ever expanding number of international science experiments being conducted aboard the station in a peaceful and collaborative manner to unite the nations of the world in this magnificent engineering achievement.

Rollback of the RSS to the parked position was completed at 5:56 PM during the T minus 11 hour hold during the launch countdown. The massive cocoon-like structure is 130 feet tall and provides weather protection and access for technicians to work on the shuttle and cargo in the payload bay. Installation and work on the STS 129 payload had already been completed and the payload bay doors were closed.

The protective Rotating Service Structure is about halfway through its 25 minute long rollback at dusk on 15 November 2009 to expose Atlantis for launch at Kennedy Space Center Pad 39 A. Credit: Ken Kremer

The countdown continues smoothly towards an afternoon liftoff at 2:28 PM EST. The STS-129 Space Shuttle Commander is Charles O. Hobaugh (third flight). Pilot is Barry E. Wilmore (first flight). The four Mission Specialists are Leland Melvin (second flight), Randy Bresnik (first flight), Mike Foreman (second flight) and Robert L. Satcher Jr. (first flight).

Watch continuous NASA live launch commentary on NASA TV and the Web

Here is a timeline of events on what to expect for Launch day:
4:30 AM Crew wake up
5 AM Crew breakfast
5:03 Tanking Begins. Chill down propellant transfer lines
5:13 Begin loading the external fuel tank with about 500,000 gallons of cryogenic propellants
5:30 Crew final medical checks
6:03 Liquid Hydrogen “fast fill” begins
7:18 Liquid Hydrogen “topping” begins (gaseous hydrogen vent valve cyclng)
8:03 Complete filling the external tank with its flight load of liquid hydrogen and liquid oxygen propellants
Final Inspection Team proceeds to launch pad
8:30 Ascent team on console in Mission Control
9:30 Launch coverage begins on NASA TV
10:05 Astronauts don flight suits
10:38 Crew departs Operations and Checkout Building for pad 39 A
Complete closeout preparations in the White Room
Check cockpit switch configurations
11:08 Flight crew begins to board Atlantis
Astronauts perform air-to-ground voice checks with Launch and Mission Control
12:13 PM Begin to close Atlantis’ crew hatch
Perform hatch seal and cabin leak checks
12:53 Complete White Room closeout
Closeout crew moves to fallback area
1:13 Enter 10-minute hold at T-20 minutes
NASA test director conducts final launch team briefings
1:23 Resume countdown at T-20 minutes
Transition the orbiter’s onboard computers to launch configuration
Start fuel cell thermal conditioning
Close orbiter cabin vent valves
Transition backup flight system to launch configuration
1:34 Countdown enters estimated 45-minute hold at T-9 minutes
Launch director, Mission Management Team and NASA test director conduct final polls for “go/no go” to launch
2:19 Resume countdown at T-9 minutes
Start automatic ground launch sequencer (T-9 minutes)
Retract orbiter crew access arm (T-7:30)
Start APU recorders (T-6:15)
Start auxiliary power units (T-5)
Terminate liquid oxygen replenish (T-4:55)
Start orbiter aerosurface profile test (T-3:55)
Start main engine gimbal profile test (T-3:30)
Pressurize liquid oxygen tank (T-2:55)
Begin retracting the gaseous oxygen vent arm (T-2:50)
Fuel cells to internal reactants (T-2:35)
Pressurize liquid hydrogen tank (T-1:57)
Deactivate bi-pod heaters (T-1:52)
Deactivate solid rocket booster joint heaters (T-0:50 seconds)
Orbiter transfers from ground to internal power (T-0:50 seconds)
Ground launch sequencer go for auto sequence start (T-0:31 seconds)
Booster gimbal profile (T-0:21 seconds)
Ignition of three space shuttle main engines (T-6.6 seconds)
Booster ignition and liftoff (T-0)

2:28:04 PM Preferred launch time

Read my earlier KSC reports on launch attempts for Atlantis and Atlas here:

Clock Ticking for Shuttle Atlantis on Critical Resupply Mission

Atlas Launch halted by ORCA; Shuttle Atlantis Next in Line

Ken Kremer’s website

November 15, 2009December 24, 2015 by Nicholos Wethington

Designing a Better Astronaut Glove

If you can build a better mousetrap, then you can certainly build a better glove for astronauts! Making a glove that both protects the hands of the astronauts in the harsh environment of space or on the Moon, and allowing them the dexterity to manipulate tools is a tough challenge for NASA. That’s why they are holding the second Astronaut Glove Challenge on November 19th, with a $400,000 prize for the best glove.

The layers of protection that an astronaut glove needs to have to shield against micrometeorites in space and insulate the hand of the wearer make for one rigid glove. The gloves are also pressurized, which makes them more rigid and further detracts from the mobility of an astronaut. NASA has held one previous competition to see who could build a better glove, in 2007, and the winner was Peter Homer, a former aerospace engineer. He took home the $200,000 prize last time, and is expected to return this year to compete against at least one other team. To read more about his story and see a video of his glove in operation, visit NASA’s page about him. Homer was also featured on Wired Magazine’s “Geek Dad” series, and a video interview is available here.

The last competition involved performing a series of tasks inside of a box that is under vacuum to measure how fatiguing to the fingers the glove was. The inside bladder of the glove was subjected to a burst test, in which it was pressurized to the point at which it bursts. The amount of force required to bend each finger of the glove was also measured.

These same rules will apply in this year’s competition, but the added challenge will be to perform all of these tests inside of an improved thermal micrometeorite garment, the outside layer of the glove that protects the astronaut’s hand from damage. This is basically a complete glove that is ready for operation in space.

NASA has been holding several challenges with some hefty prizes to incite development in space-related technology. The Centennial Challenge program most recently gave away prizes for the Power Beaming Challenge and the Lunar Lander Challenge. The prize will be provided by NASA, but the competition is managed by Volanz Aerospace Inc. of Owings, Md. and sponsored by Secor Strategies, LLC of Titusville, Fla.

Good luck to all the competitors, and may the best glove win!

Source: NASA, Astronaut Glove Challenge

November 15, 2009February 2, 2017 by Abby Cessna

Who were the Space Monkeys?

Albert II in preparation for his historic flight. Image Credit: NASA

The Space Age was an era of unprecedented technological development. In addition to developing the rockets and modules needed to put astronauts into space, considerable resources were also dedicated towards testing the effects spaceflight would have on the human body. In order to do this, test subjects needed to be selected that were physiologically similar enough to human beings.

For NASA, the Russians, and many space programs that have followed, the choice was to send simians (aka. monkeys) into space. While space missions would rely other animals to test the effects spaceflight would have on living organisms (such as dogs, guinea pigs, and even insects), monkeys were the most-widely used since they are more closely related to humans.

Background:

In the late 1940s, both NASA and the Soviet Space Program were working diligently to try and develop space launch capability. However, a going concern at the time was the risks posed by crewed spaceflight. At the time, the effects of weightlessness on the human body were unknown, and whether or not a human could even survive exposure was the subject of much scientific debate.

American Space Monkeys:

Russian Space Monkeys:

Other Space Agencies:

Although men have gone to space, they were not the first ones there. Scientists have sent a number of different animals up into space including monkeys. Both Russia and America sent monkeys into space. This is because scientists wanted to determine what the biological effects of space travel were before they sent humans up. While Russia only used rhesus monkeys, the US used many different species including rhesus monkeys, squirrel monkeys, cynomolgus monkeys, pig-tailed macaques, and chimpanzees. Even France sent up two monkeys into space during the 1960’s. These animals were both recovered alive.

Many of the monkeys sent up into space died either on impact or in space. The US sent four monkeys into space named Albert, all of which died. The first monkey that actually passed the Karman line and made it into space was Albert II. He was sent up in 1949 and died on impact.

Gordo, who was also known as Old Reliable, was sent into space in 1958. A squirrel monkey, he was chosen because of the similarity of the species to the human body. Gordo was lost on impact and neither him nor the shuttle was recovered; however, scientists were heartened by the mission because they believed it helped prove that humans could survive in space. The first monkeys to survive space were Able and Miss Baker who were sent up in 1959.

The Russians sent dogs up into space in addition to monkeys, which is why they did not send nearly as many monkeys into space as America did. Thus the first monkey that they actually sent into space was not until 1983. The monkeys that the Russians sent into space were named according to the letters of the alphabet. One of these monkeys – Dryoma – who went to space in 1987 – was later given to Fidel Castro. The last monkeys the Russians sent up into space were Lapik and Multik whe went up in 1997. Both of them survived the mission, but Multik had a heart attack a day after the flight during medical tests.

One of the most famous monkeys ever sent into space was Ham the Chimp. He was trained to operate the controls of the spaceship becoming the first animal to not just be a passenger. Ham was recovered safe after his capsule crashed in the Atlantic Ocean. Scientists were able to determine that astronauts would then be able to operate instruments in space and Alan Shepard went into space several months after Ham.

We have written many interesting articles about space monkeys and animals sent into space here at Universe Today. Here’s Russia to send monkey to Mars, Who was the First Monkey to go into Space?, 50th Anniversary of Historic Space Monkey Flight, What Animals have been to Space?, Who was the First Animal to go into Space?, Who was the First Dog to go into Space?

For more information, check out animals in space and monkeys in space fifty years later.

Astronomy Cast has an episode on spacesuits.

Sources:

November 15, 2009April 26, 2016 by Abby Cessna

Famous Astronomers

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Throughout the centuries, many astronomers have made incredible discoveries and contributions to science. I cannot do justice to all of them by any means, so I will concentrate on a few of the most famous astronomers throughout history.

Claudius Ptolemy was an astronomer and mathematician in Alexandria. He wrote an extensive treatise on astronomy known as the Almagest. It mapped out complex movements of the stars and planets. His model was geocentric, meaning he placed the Earth at the center of the universe. This geocentric model was widely accepted for more than a thousand years in many cultures. It is often known as the Ptolemaic model.

Galileo Galilei lived between 1564 and 1642 in Italy. He was a physicist and astronomer. Galileo created the first telescope, although his first model was very weak. His next one though was strong enough that he could see craters on the Moon, four of Jupiter’s moons, anda number of stars in the Milky Way.

The Polish astronomer Nicolas Copernicus lived between 1473 and 1543. He is famous for his theory tha the Sun is the center of the universe, not the Earth. His theory is often known as the Copernican model. It was years before his model became widely accepted though.

Johannes Kepler was a famous German astronomer who lived between 1571 and 1630. He was the first person to identify planetary motion. Kepler is probably most famous for his three laws of planetary motion, which describe the motion of two celestial bodies such as a planet and its star.

Edmond Halley lived between 1656 and 1742. He predicted the orbit of the Halley Comet, which was named in his honor. He also published an extensive catalog of stars and created a diving bell, which he improved throughout the years.

Sir Friedrich William Herschel, often known as William Herschel, was a famous astronomer of the late18th to the early 19th century. He is famous for having discovered the plant Uranus and two of its moons. He also made over 400 telescopes during his life. Herschel discovered two of Saturn’s moons – Mimas and Enceladus.

Clyde Tombaugh is an American astronomer who is best known for discovering Pluto in 1930. Pluto was considered a planet for 76 years until it was reclassified as a dwarf planet. He did not actually have any astronomy degrees until after he discovered Pluto when he studied astronomy. He also discovered a number of asteroids.

Universe Today has more articles on astronomers are people too and artist creates portrait gallery of astronomers.

If you are looking for more information, check out famous astronomers and influential astronomers

Astronomy Cast has an episode on building a career in astronomy.

Sources:
NASA: Cosmology
NASA: Kepler
NASA: Edmond Halley
SEDS.org
NASA: Clyde Tombaugh

November 15, 2009December 24, 2015 by Jean Tate

Electron Mass

3d model of electron orbitals, based on the electron cloud model. Credit: Wikipedia Commons/Particia.fidi

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The mass of the electron, or the electron’s mass, written as m_e, is 9.109 382 15(45) x 10^-31 kg. This is the “CODATA recommended value”. It was published in March 2007, and is referred to as the 2006 CODATA recommended value.

Some background: CODATA stands for Committee on Data for Science and Technology. Per NIST (the US National Institute for Standards and Technology), “CODATA was established in 1966 as an interdisciplinary committee of the International Council of Science (ICSU), formerly the International Council of Scientific Unions. It seeks to improve the compilation, critical evaluation, storage, and retrieval of data of importance to science and technology. The CODATA Task Group on Fundamental Constants was established in 1969. Its purpose is to periodically provide the international scientific and technological communities with an internationally accepted set of values of the fundamental physical constants and closely related conversion factors for use worldwide. The first such CODATA set was dated 1973, the second 1986, the third 1998, the fourth 2002, and the fifth (the current set) 2006.”

The mass of the electron is one of the fundamental physical constants, so called because they are widespread in theories of physics, and because they are widely used in the application of those theories to other branches of science and to practical uses (such as engineering). Four of the other fundamental physical constants are c (speed of light in a vacuum), e (the charge of the electron), h (Plank’s constant), and α (fine structure constant).

The method used for measuring m_e is to measure the Rydberg constant (R_∞) and calculate m_e from it ( m_e = 2R_∞h/(cα² ); the Rydberg constant is, in the words of the paper (by Peter J. Mohr, Barry N. Taylor, David B. Newell) in which the 2006 CODATA recommended values were published “can be accurately determined by comparing measured resonant frequencies of transitions in hydrogen (H) and deuterium (D) to the theoretical expressions for the energy level differences in which it is a multiplicative factor.” For more details, refer to the paper itself.

Given that it is a fundamental physical constant, no surprise that Universe Today has some articles on it! For example Are the Laws of Nature the Same Everywhere in the Universe, and Fermilab putting the Squeeze on Higgs Boson.

Here are two Astronomy Cast episodes in which the electron mass figures prominently Electromagnetism, and Energy Levels and Spectra.

Sources:
NIST
Wikipedia – Electron Rest Mass
Wikipedia – Rydberg constant

November 15, 2009December 24, 2015 by Jean Tate

Baryon

Particle Collider — Today, CERN announced that the LHCb experiment had revealed the existence of two new baryon subatomic particles. Credit: CERN/LHC/GridPP

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Particles made up of three quarks are called baryons; the two best known baryons are the proton (made up of two up quarks and one down) and the neutron (two down quarks and one up). Together with the mesons – particles comprised of a quark and an antiquark – baryons form the hadrons (you’ve heard of hadrons, they’re part of the name of the world’s most powerful particle collider, the Large Hadron Collider, the LHC).

Because they’re made up of quarks, baryons ‘feel’ the strong force (or strong nuclear force as it is also called), which is mediated by gluons. The other kind of particle which makes up ordinary matter is leptons, which are not – as far as we know – made up of anything (and as they do not contain quarks, they do not participate in the strong interaction … which is another way of saying they do not experience the strong force); the electron is one kind of lepton. Baryons and leptons are fermions, so obey the Pauli exclusion principle (which, among other things, says that there can be no more than one fermion in a particular quantum state at any time … and ultimately why you do not fall through your chair).

In the kinds of environments we are familiar with in everyday life, the only stable baryon is the proton; in the environment of the nuclei of most atoms, the neutron is also stable (and in the extreme environment of a neutron star too); there are, however, hundreds of different kinds of unstable baryons.

One big, open question in cosmology is how baryons were formed – baryogenesis – and why are there essentially no anti-baryons in the universe. For every baryon, there is a corresponding anti-baryon … there is, for example, the anti-proton, the anti-baryon counterpart to the proton, made up of two up anti-quarks and one down anti-quark. So if there were equal numbers of baryons and anti-baryons to start with, how come there are almost none of the latter today?

Astronomers often use the term ‘baryonic matter’, to refer to ordinary matter; it’s a bit of a misnomer, because it includes electrons (which are leptons) … and it generally excludes neutrinos (and anti-neutrinos), which are also leptons! Perhaps a better term might be matter which interacts via electromagnetism (i.e. feels the electromagnetic force), but that’s a bit of a mouthful. Non-baryonic matter is what (cold) dark matter (CDM) is composed of; CDM does not interact electromagnetically.

The Particle Data Group maintains summary tables of the properties of all known baryons. A relatively new area of research in astrophysics (and cosmology) is baryon acoustic oscillations (BAO); read more about it at this Los Alamos National Laboratory website …

… and in the Universe Today article New Search for Dark Energy Goes Back in Time. Other Universe Today stories featuring baryons explicitly include Is Dark Matter Made Up of Sterile Neutrinos?, and Astronomers on Supernova High Alert.

Sources:
Wikipedia
Hyperphysics

November 15, 2009December 24, 2015 by Jean Tate

What is Alpha Radiation?

Alpha radiation is another name for the alpha particles emitted in the type of radioactive decay called alpha decay. Alpha particles are helium-4 (⁴He) nuclei.

Radioactivity was discovered by Becquerel, in 1896 (and one of the units of radioactivity – the becquerel – is named after him); within a few years it was discovered (Rutherford gets most of the credit, though others contributed) that there are actually three kinds of radioactivity, which were given the exciting names alpha (radiation), beta (radiation), and gamma (radiation; there are some other, rare, kinds of radioactive decay, the most important being positron, or positive beta). Rutherford (with some help) worked out that alpha radiation is actually the nuclei of helium … by allowing alpha radiation to go through the thin walls of an evacuated glass tube, and later analyzing the gas in the tube spectroscopically).

Some fun facts about alpha radiation:

* alpha radiation is the least penetrating (of alpha, beta, and gamma); typically it goes no more than a few cm in air

* like all kinds of radioactive decay, alpha decay occurs because the final state of the nucleus (the one decaying) has a lower energy than the initial one (the difference is the energy of the emitted alpha particle, both its binding energy and its kinetic energy)

* alpha decay involves both strong and electromagnetic interactions (or forces), unlike beta and gamma decay

* the key to the specifics of alpha decay is the quantum effect called tunneling; Gamow worked this out, in 1928

* only heavier nuclides can undergo alpha decay; the lightest are light isotopes of tellurium

* alpha radiation played a star role in the development of our understanding of the nature of atoms … Rutherford, in 1909, aimed a beam of alpha radiation at a piece of thin gold foil, and counted the number of particles which were deflected at each angle; from this he deduced that the atom has a very small nucleus (with all the positive charge, and nearly all its mass).

For more background on alpha radiation, check out the Jefferson Lab’s What are alpha rays? How are they produced?.

There are many ways alpha radiation can turn up in Universe Today articles; for example, in NASA May Have to Revamp Science Plans Without RTGs, alpha radiation is essential to RTGs; and in Opportunity Rover Sidelined by Charged Particle Hit, alpha radiation is what’s used to help determine the elemental composition of samples.

Nucleosynthsis: Elements from Stars and Cosmic Rays are two Astronomy Cast episodes which also cover alpha radiation.

Source: Wikipedia

November 15, 2009December 24, 2015 by Jean Tate

Sirius B

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Sirius B is the name of the fainter, smaller, less massive star in the Sirius binary system (the brighter, larger, more massive one is Sirius A, or just Sirius). It was hypothesized to exist almost eighteen years before it was actually observed!

Details: Bessel – yep, the guy who Bessel functions are named after – analyzed data on the position of Sirius (Bessel was the one who first observed stellar parallax), in particular its proper motion, and concluded – in 1844 – that there was an unseen companion star (the same principle used to infer the existence of Neptune, around the same time). In 1862 Alvan Clark saw this companion, using the 18.5″ refracting telescope he’d just built (quite a feat; Sirius B is ~10 magnitudes fainter than Sirius A, and separated by only a few arcseconds).

Sirius B is a white dwarf, one of the three “classics”, discovered to be white dwarf stars in the early years of the 20th century (Sirius B was the second to be discovered – 40 Eridani B had been found much earlier, and Procyon B was also hypothesized by Bessel (in 1844) though not observed until much later (in 1896)). It is one of the most massive white dwarfs so far discovered; its mass is the same as that of the Sun (approximately). Like all white dwarfs, it is small (it has a radius of only 0.008, compared with the Sun’s, which makes it smaller than the Earth!); like most seen so far, it is hot (approx 25,000 K).

Sirius B was likely a five sol B star as recently as 60 million years ago (when it was, coincidentally, approximately 60 million years old!), when it entered first a hydrogen shell burning, then a helium shell burning, stage, shed most of its mass (and enriching its companion with lots of ‘metals’ in the process), and shrank to become a white dwarf. There is no fusion taking place in Sirius B’s degenerate carbon/oxygen core (which makes up almost all of the star; there is a thin, non-degenerate, hydrogen atmosphere … this is what we see), so it is slowly cooling (it cools so slowly because it has such a small surface area).

Packing such a large mass into such a small volume means that Sirius B’s surface gravity is huge … so great in fact that it serves as an excellent test of one of the predictions of Einstein’s theory of General Relativity: gravitational redshift (this was first observed in the lab in 1959, by Pound and Rebka). The most recent observation of this gravitational redshift was by the Hubble, in 2005, as described in the Universe Today article Sirius’ White Dwarf Companion Weighed by Hubble.

Other Universe Today stories about Sirius B include White Dwarf Theories Get More Proof, and this 2005 What’s Up This Week one.

Astronomy Cast has two episodes related to Sirius B, Dwarf Stars, and Binary Stars.

References:
http://www.solstation.com/stars/sirius2.htm
http://en.wikipedia.org/wiki/Sirius