Posted on by Jean Tate

Stunning Science Using Nature’s Telescope

3Star-birth in SMM J2135-0102 (Credit: M. Swinbank et al./Nature, ESO, APEX; NASA, ESA, SMA)

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Einstein started it all, back in 1915.

Eddington picked up the ball and ran with it, in 1919.

And in the last decade or so astronomers have used a MACHO to OLGE CASTLES … yes, I’m talking about gravitational lensing.

Now LABOCA and SABOCA are getting into the act, using Einstein’s theory of general relativity to cast a beady eye upon star birth most fecund, in a galaxy far, far away (and long, long ago).

APEX at Chajnantor (Andreas Lundgren)

How galaxies evolved is one of the most perplexing, challenging, and fascinating topics in astrophysics today. And among the central questions – as yet unanswered – are how quickly stars formed in galaxies far, far away (and so long, long ago), and how such star formation differed from that which we can study, up close and personal, in our own galaxy (and our neighbors). There are lots of clues to suggest that star formation happened very much faster long ago, but because far-away galaxies are both dim and small, and because Nature drapes veils of opaque dust over star birth, there’s not much hard data to put the numerous hypotheses to the test.

Until last year that is.

“One of the brightest sub-mm galaxies discovered so far,” say a multi-national, multi-institution team of astronomers, was “first identified with the LABOCA instrument on APEX in May 2009” (you’d think they’d give it a name like, I don’t know, “LABOCA’s Stunner” or “APEX 1”, but no, dubbed “the Cosmic Eyelash”; formally it’s called SMMJ2135-0102). “This galaxy lies at [a redshift of] 2.32 and its brightness of 106 mJy at 870 μm is due to the gravitational magnification caused by a massive intervening galaxy cluster,” and “high resolution follow-up with the sub-mm array resolves the star-forming regions on scales of just 100 parsecs. These results allow study of galaxy formation and evolution at a level of detail never before possible and provide a glimpse of the exciting possibilities for future studies of galaxies at these early times, particularly with ALMA.” Nature’s telescope giving astronomers ALMA-like abilities, for free.

OK, so what did Mark Swinbank and his colleagues find? “The star-forming regions within SMMJ2135-0102 are ~100 parsecs across, which is 100 times larger than dense giant molecular cloud (GMC) cores, but their luminosities are approximately 100 times higher than expected for typical star-forming regions. Indeed, the luminosity densities of the star-forming regions within SMMJ2135-0102 are comparable to dense GMC cores, but with luminosities ten million times larger. Thus, it is likely that each of the star-forming regions in SMMJ2135-0102 comprises ~ten million dense GMC cores.” That’s pretty mind-blowing; imagine the Orion Nebula (M42, approximately 400 parsecs distant) as one of these star-forming regions!

James Dunlop of the University of Edinburgh suggests that such galaxies as SMMJ2135-0102 formed stars so abundantly because the galaxies still had plenty of gas – the raw material for making stars – and the gravity of the galaxies had had enough time to pull the gas together into cold, compact regions. Before about 10 billion years ago, gravity hadn’t yet drawn enough clumps of gas together, while at later times most galaxies had already run out of gas, he suggests.

But I’m saving the best for last: “the energetics of the star-forming regions within SMMJ2135-0102 are unlike anything found in the present day Universe,” Swinbank et al. write (now there’s an understatement if ever I’ve heard one!), “yet the relations between size and luminosity are similar to local, dense GMC cores, suggesting that the underlying physics of the star-forming processes is similar. Overall, these results suggest that the recipes developed to understand star-forming processes in the Milky Way and local galaxies can be used to model the star formation processes in these high-redshift galaxies.” It’s always good to get confirmation that our understanding of the physics at work so long ago is consistent and sound.

Einstein would have been delighted, and Eddington too.

Sources: “Intense star formation within resolved compact regions in a galaxy at z = 2.3” (Nature), “The Properties of Star-forming Regions within a Galaxy at Redshift 2” (ESO Messenger No. 139), Science News, SciTech, ESO. My thanks to debreuck (ESO’s Carlos De Breuck?) for setting the record straight re the name.

Posted on by Jean Tate

Universe Puzzle No. 8

As with last week’s Universe Puzzle, something that cannot be answered by five minutes spent googling, a puzzle that requires you to cudgel your brains a bit, and do some lateral thinking. This is a puzzle on a “Universal” topic – astronomy and astronomers; space, satellites, missions, and astronauts; planets, moons, telescopes, and so on.

This puzzle is actually from Universe Today reader, Vino; thanks Vino!

What comes next in the sequence?

0.789, 0.854, 0.941

UPDATE: Answer has been posted below.

1.091

These are the periods, in days, of the transiting extrasolar planets so far discovered, in ascending order (source): WASP-19b, CoRoT-7b, WASP-18b, and WASP-12b.

Check back next week for another Universe Puzzle!

Posted on by Jean Tate

Andromeda’s Double Nucleus – Explained at Last?

M31's nucleus (Credit: WF/PC, Hubble Space Telescope)


In 1993, the Hubble Space Telescope snapped a close-up of the nucleus of the Andromeda galaxy, M31, and found that it is double.

In the 15+ years since, dozens of papers have been written about it, with titles like The stellar population of the decoupled nucleus in M 31, Accretion Processes in the Nucleus of M31, and The Origin of the Young Stars in the Nucleus of M31.

And now there’s a paper which seems, at last, to explain the observations; the cause is, apparently, a complex interplay of gravity, angular motion, and star formation.

[/caption]
It is now reasonably well-understood how supermassive black holes (SMBHs), found in the nuclei of all normal galaxies, can snack on stars, gas, and dust which comes within about a third of a light-year (magnetic fields do a great job of shedding the angular momentum of this ordinary, baryonic matter).

Also, disturbances from collisions with other galaxies and the gravitational interactions of matter within the galaxy can easily bring gas to distances of about 10 to 100 parsecs (30 to 300 light years) from a SMBH.

However, how does the SMBH snare baryonic matter that’s between a tenth of a parsec and ~10 parsecs away? Why doesn’t matter just form more-or-less stable orbits at these distances? After all, the local magnetic fields are too weak to make changes (except over very long timescales), and collisions and close encounters too rare (these certainly work over timescales of ~billions of years, as evidenced by the distributions of stars in globular clusters).

That’s where new simulations by Philip Hopkins and Eliot Quataert, both of the University of California, Berkeley, come into play. Their computer models show that at these intermediate distances, gas and stars form separate, lopsided disks that are off-center with respect to the black hole. The two disks are tilted with respect to one another, allowing the stars to exert a drag on the gas that slows its swirling motion and brings it closer to the black hole.

The new work is theoretical; however, Hopkins and Quataert note that several galaxies seem to have lopsided disks of elderly stars, lopsided with respect to the SMBH. And the best-studied of these is in M31.

Hopkins and Quataert now suggest that these old, off-center disks are the fossils of the stellar disks generated by their models. In their youth, such disks helped drive gas into black holes, they say.

The new study “is interesting in that it may explain such oddball [stellar disks] by a common mechanism which has larger implications, such as fueling supermassive black holes,” says Tod Lauer of the National Optical Astronomy Observatory in Tucson. “The fun part of their work,” he adds, is that it unifies “the very large-scale black hole energetics and fueling with the small scale.” Off-center stellar disks are difficult to observe because they lie relatively close to the brilliant fireworks generated by supermassive black holes. But searching for such disks could become a new strategy for hunting supermassive black holes in galaxies not known to house them, Hopkins says.

Sources: ScienceNews, “The Nuclear Stellar Disk in Andromeda: A Fossil from the Era of Black Hole Growth”, Hopkins, Quataert, to be published in MNRAS (arXiv preprint), AGN Fueling: Movies.

Posted on by Jean Tate

Magnetic Fields in Spiral Galaxies – Explained at Last?

M51 (Hubble) overlaid by 6cm radio intensity contours and polarization vectors (Effelsberg and VLA) Credit: MPIfR Bonn

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That spiral galaxies have magnetic fields has been known for well over half a century (and predictions that they should exist preceded discovery by several years), and some galaxies’ magnetic fields have been mapped in great detail.

But how did these magnetic fields come to have the characteristics we observe them to have? And how do they persist?

A recent paper by UK astronomers Stas Shabala, James Mead, and Paul Alexander may contain answers to these questions, with four physical processes playing a key role: infall of cool gas onto the disk, supernova feedback (these two increase the magnetohydrodynamical turbulence), star formation (this removes gas and hence turbulent energy from the cold gas), and differential galactic rotation (this continuously transfers field energy from the incoherent random field into an ordered field). However, at least one other key process is needed, because the astronomers’ models are inconsistent with the observed fields of massive spiral galaxies.

“Radio synchrotron emission of high energy electrons in the interstellar medium (ISM) indicates the presence of magnetic fields in galaxies. Rotation measures (RM) of background polarized sources indicate two varieties of field: a random field, which is not coherent on scales larger than the turbulence of the ISM; and a spiral ordered field which exhibits large-scale coherence,” the authors write. “For a typical galaxy these fields have strengths of a few μG. In a galaxy such as M51, the coherent magnetic field is observed to be associated with the optical spiral arms. Such fields are important in star formation and the physics of cosmic rays, and could also have an effect on galaxy evolution, yet, despite their importance, questions about their origin, evolution and structure remain largely unsolved.”

This field in astrophysics is making rapid progress, with understanding of how the random field is generated having become reasonably well-established only in the last decade or so (it’s generated by turbulence in the ISM, modeled as a single-phase magnetohydrodynamic (MHD) fluid, within which magnetic field lines are frozen). On the other hand, the production of the large-scale field by the winding of the random fields into a spiral, by differential rotation (a dynamo), has been known for much longer.

The details of how the ordered field in spirals formed as those galaxies themselves formed – within a few hundred million years of the decoupling of baryonic matter and radiation (that gave rise to the cosmic microwave background we see today) – are becoming clear, though testing these hypotheses is not yet possible, observationally (very few high-redshift galaxies have been studied in the optical and NIR, period, let alone have had their magnetic fields mapped in detail).

“We present the first (to our knowledge) attempt to include magnetic fields in a self-consistent galaxy formation and evolution model. A number of galaxy properties are predicted, and we compare these with available data,” Shabala, Mead, and Alexander say. They begin with an analytical galaxy formation and evolution model, which “traces gas cooling, star formation, and various feedback processes in a cosmological context. The model simultaneously reproduces the local galaxy properties, star formation history of the Universe, the evolution of the stellar mass function to z ~1.5, and the early build-up of massive galaxies.” Central to the model is the ISM’s turbulent kinetic energy and the random magnetic field energy: the two become equal on timescales that are instantaneous on cosmological timescales.

The drivers are thus the physical processes which inject energy into the ISM, and which remove energy from it.

“One of the most important sources of energy injection into the ISM are supernovae,” the authors write. “Star formation removes turbulent energy,” as you’d expect, and gas “accreting from the dark matter halo deposits its potential energy in turbulence.” In their model there are only four free parameters – three describe the efficiency of the processes which add or remove turbulence from the ISM, and one how fast ordered magnetic fields arise from random ones.

Are Shabala, Mead, and Alexander excited about their results? You be the judge: “Two local samples are used to test the models. The model reproduces magnetic field strengths and radio luminosities well across a wide range of low and intermediate-mass galaxies.”

And what do they think is needed to account for the detailed astronomical observations of high-mass spiral galaxies? “Inclusion of gas ejection by powerful AGNs is necessary in order to quench gas cooling.”

SKA central region with separate core stations for the two aperture arrays for low and mid frequencies and for the dish array. Graphics: Xilostudios and SKA Project Development Office

It goes without saying that the next generation of radio telescopes – EVLA, SKA, and LOFAR – will subject all models of magnetic fields in galaxies (not just spirals) to much more stringent tests (and even enable hypotheses on the formation of those fields, over 10 billion years ago, to be tested).

Source: Magnetic fields in galaxies: I. Radio disks in local late-type galaxies

Posted on by Tammy Plotner

Weekend SkyWatcher’s Forecast: April 2-4, 2010

Greetings, fellow SkyWatchers! Have you been out enjoying the Sun? You better be, because the Sun has been enjoying you and putting on quite a show! Once it sets, be sure to look for both Venus and Mercury decorating the western skyline. With the Moon gone off the early evening scene, it’s also time to take on a couple of new galactic open cluster studies to tease your eye with photons! Whenever you’re ready, I’ll see you in the dark…

April 2, 2010 – On this date in 1889, the Harvard Observatory’s 13″ refractor arrived at Mt. Wilson. Just one month later, it went into astronomical service at Lick Observatory, located at Mt. Hamilton. It was here that the largest telescopes in the world resided from 1908 to 1948 – the 60″ for the first decade, then the 100″. This latter mirror is still the largest solid piece ever cast in plate glass, and weighed 4.5 tons. Would you believe it’s just 13″ thick?

This date in 1845, the first photograph of the Sun was taken. Although solar photography and observing is the domain of properly filtered telescopes, no special equipment is necessary to see some effects of the Sun, only the correct conditions. Right now Earth’s magnetosphere and magnetopause (the point of contact) are positioned correctly to interact with the Sun’s influencing interplanetary magnetic field (IMF), and the plasma stream that flows past us as the solar wind. During the time around equinox, this leaves the door wide open for one of the most awesome signs of spring – aurora! Visit the Geophysical Institute to sign up for aurora alerts, and use their tools to help locate the position of Earth’s auroral oval.


So is the Sun active right now? You betcha’. According to Spaceweather.com: “Amateur astronomers around the world are monitoring a huge prominence rising over the Sun’s northeastern limb. Magnetic fields underpinning this magnificent structure are in a state of fairly rapid motion, pulling the plasma to and fro, offering a different profile to every observer. The whole thing could become unstable and collapse.”

After you’ve enjoyed today’s Sun, be sure to watch as it sets for the brilliant appearance of Venus. Look closely to the northwest and you’ll see another planet, too. Mercury has come round from behind the Sun and is visible for a short time. If you don’t spot it at twilight, don’t despair. By week’s end, the two planets will be just 3 degrees apart!

April 3, 2010 – Tonight let’s try for a scattered open cluster, NGC 2281 (RA 06 48 18 Dec +41 05 00) toward the west in Auriga. At magnitude 5.4, NGC 2281 should be visible as a nebulous mist in binoculars on a dark night, but you’ll need a scope and high power to darken the sky enough to see the bright members found near its core.


NGC 2281 is around 1,500 light-years distant and 50 million years old. It can best be found by extending a line from Capella to Beta Aurigae an equal distance east to a pair of 5th magnitude stars separated by a finger-width. NGC 2281 lies less than a degree southeast of the eastern member of this pair (58 Aurigae). When studied photometrically, NGC 2281’s binary stars were found to congregate more toward the center of the cluster, and with more intensity than for single stars alone. With a population of no more than 60 stars, the binaries far outnumber their counterparts!

April 4, 2010 – Today we celebrate the 1809 birth on this date of astronomer Benjamin Peirce. Peirce was a professor of astronomy and mathematics for nearly 40 years and contributed greatly to the discovery of Neptune.

If you like challenging planetary nebulae studies, here’s a good one to try tonight – NGC 2610 (RA 08 33 23 Dec –16 08 58) near the Hydra/Puppis/Pyxis border.


At 13th magnitude, it’s not for the beginner, but a worthy study for seasoned veterans. Its position near two 7th magnitude stars will help reveal its location at low power. Magnify to catch a slightly elliptical shell, a stellar point on its northeast edge, and a wink of a central star. Note NGC 2610 is also cataloged as Herschel IV 65 – another to add to your ‘‘Herschel Hit List!’’

Have a terrific holiday weekend!

This week’s awesome images are: Hooker Telescope courtesy of NASA, latest H-Alpha image courtesy of SOHO, NGC 2281 and NGC 2610 from Palomar Observatory, courtesy of Caltech. We thank you so much!

Posted on by Tammy Plotner

NGC 1097 Galaxy Jets: They Aren’t Just For Breakfast Anymore

Some 45 million light years away in the direction of the constellation of Fornax, a supermassive black hole is consuming its breakfast… and it doesn’t want just toast and tea. It has a hungry belly and the energetic area surrounding the central black hole is super-heated through its interaction with dust, gas, and other matter. Oh, dear. What can that matter be? Try a smaller galaxy that dared to get too close…

NGC1097 belongs a special class of galaxies called Seyfert – those that produce a specific type of spectrum and are thought to contain active galactic nuclei with super massive black holes. What makes this galaxy even more interesting is the very faint optical “jets” that may be the remnants of a smaller galaxy interaction many years ago.

Like a lingering smear of marmalade or a trail of toast crumbs, these optical jets leave visual and photographic clues as to their origin. In a deep search for neutral hydrogen gas associated with the faint optical “jets” of NGC 1097, researchers using the Very Large Array detected an H I source coincident with a small edge-on spiral or irregular galaxy (NGC 1097B) 12′ southwest of NGC 1097, situated between two jets. In addition, two other sources are noted – but not associated with the optical jets themselves. Click here for full size color image.

Could it be bacon?

According to James Higdon and John Wallin; “The jets’ radio-X-ray spectral energy distribution is most consistent with starlight. However, from their morphology, optical/near-infrared colors, and lack of H I, we argue that the jets are not tidal tails drawn out of NGC 1097’s disk or stars stripped from the elliptical companion NGC 1097A. We also reject in situ star formation in ancient radio jets as this requires essentially 100% conversion of gas into stars on large scales. Instead, we conclude that the jets represent the captured remains of a disrupted dwarf galaxy that passed through the inner few kiloparsecs of NGC 1097’s disk.

We present N-body simulations of such an encounter that reproduce the essential features of NGC 1097’s jets: A long and narrow “X”-shaped morphology centered near the spiral’s nucleus, right-angle bends, and no discernible dwarf galaxy remnant. A series of jetlike distributions are formed, with the earliest appearing ~1.4 Gyr after impact. Well-defined X shapes form only when the more massive galaxy has a strong disk component. Ram-pressure stripping of the dwarf’s interstellar medium would be expected to occur while passing through NGC 1097’s disk, accounting for the jets’ lack of H I and H II. The remnants’ (B-V) color would still agree with observations even after ~3 Gyr of passive evolution, provided the cannibalized dwarf was low-metallicity and dominated by young stars at impact.”

Bu that’s not all that’s on the table…

“The nucleus of the nearby galaxy NGC 1097 is known to host a young, compact (r < 9 pc) nuclear star cluster, as well as a low-luminosity active galactic nucleus (AGN). It has been suggested both that the nuclear stellar cluster is associated with a dusty torus and that low-luminosity AGNs like NGC 1097 do not have the torus predicted by the unified model of AGNs. To investigate these contradictory possibilities we have acquired Gemini/T-ReCS 11.7 and 18.3 ?m images of the central few hundred parsecs of this galaxy at <45 pc angular resolution, in which the nucleus and spectacular, kiloparsec-scale star-forming ring are detected in both bands." says R.E. Mason (et al). "The small-scale mid-IR luminosity implies thermal emission from warm dust close to the central engine. Fitting of torus models shows that the observed mid-IR emission cannot be accounted for by dust heated by the central engine. Rather, the principal source heating the dust in this object is the nuclear star cluster itself, suggesting that the detected dust is not the torus of AGN unified schemes (although it is also possible that the dusty starburst itself could provide the obscuration invoked by the unified model). Comparison of Spitzer IRS and Gemini GNIRS spectra shows that, although PAH bands are strong in the immediate circumnuclear region of the galaxy, PAH emission is weak or absent in the central 19 pc. The lack of PAH emission can probably be explained largely by destruction/ionization of PAH molecules by hard photons from the nuclear star cluster. If NGC 1097 is typical, PAH emission bands may not be a useful tool with which to find very compact nuclear starbursts even in low-luminosity AGNs." And starbursts as recently as 5 years ago from this early rising Seyfert are definitely on the menu... "We report evidence of a recent burst of star formation located within 9 pc of the active nucleus of NGC 1097. The observational signatures of the starburst include UV absorption lines and continuum emission from young stars observed in a small-aperture Hubble Space Telescope spectrum." says T. Storchi-Bergmann (et al). "The importance of this finding is twofold: (1) the proximity of the starburst to the active nucleus and thus its possible association with it, and (2) its obscuration by and apparent association with a dusty absorbing medium, while the broad emission lines appear unobscured, suggesting that the starburst could be embedded in a circumnuclear torus as predicted in the unified model of active galactic nuclei." Can I have eggs with that? Many thanks to NorthernGalactic member, Ken Crawford for his exclusive images. Be sure to check out Ken’s webpages at Imaging Deep Sky.

Posted on by John Carl Villanueva

What Is Static Electricity?

Fine Structure Constant

[/caption]Wonder why you sometimes get zapped when touching a doorknob especially during winter? People will tell you it’s a simple case of static electricity. But what is static electricity?

In some texts, static electricity is a term supposedly used for electricity that does not deal with moving charges. Actually, there is movement of charges. In fact, when you get zapped, charges are actually moving between your fingers and the doorknob. However, the movement is only brief compared to the current in a closed circuit.

So how do stationary charges allow people to get zapped? To understand this phenomenon, try to recall the particles that make up an atom. That’s right, the protons, neutrons, and electrons.

Of the three, electrons are easily removed from an atom since the forces that bind them to an atom are weaker than those that hold the neutrons and protons together in the atoms’ nuclei.

Now, there are some materials that easily lose their electrons compared to others. We’ve included a list below ranking some materials based on their ability to lose electrons. The one at the top has a greater tendency to lose electrons while the one at the bottom has the least.

  • human hands
  • glass
  • nylon
  • fur
  • silk
  • aluminum
  • steel
  • hard rubber
  • vinyl(PVC)
  • Teflon

Such a list is known as a triboelectric series. A true triboelectric series would have positives and negatives but we won’t go into that here.

Therefore, based on the list, if you rubbed a glass rod with a silk cloth, it is the glass rod that would lose electrons to the cloth. When this happens, the glass rod becomes positively charged, while the silk cloth (having gained excess electrons) becomes negatively charged.

Then when you draw the glass rod close to small bits of paper, the positively charged glass rod repels the electrons in the paper (pushing them to one side in the paper) and attracting the positive side. This allows the bits of paper to stick to the glass rod.

In the case of people getting zapped, they usually gain electrons when they walk across a carpeted floor. The interaction is between the carpet and the soles of their shoes but the overall charge of their bodies get affected. You can imagine them as walking negatively-charged bodies.

So, when they touch a metal door knob, the excess electrons readily leap from their hands to the metal knob and they get zapped.

Actually, static electricity is a rather lengthy physics topic that covers more than just the zapping phenomena. It includes discussions on induction, conduction, Coulomb’s Law, and electric fields, to mention a few. However, when a regular person asks, “what is static electricity?”, he most likely wants you to explain about the painful sensation he experiences upon touching a door knob.

Coulomb’s Law deals with charges. Universe Today has articles talking about the charge of the proton and the charge of the electron.

NASA also has some related stuff. Check out the following articles:
Charges
Killer Electrons

Here are two episodes at Astronomy Cast that you might want to check out as well:
Antimatter
The Search for Dark Matter

Sources:
Wikipedia
How Stuff Works
The Physics Classroom

Posted on by John Carl Villanueva

What Is Sound?

What is Sound
FA-18_Hornet_breaking_sound_barrier_(7_July_1999)_-_filtered

[/caption]Light and sound are both waves. However, the former can travel through a vacuum while the latter cannot. So what is sound and how does it propagate as a wave?

Sound is actually a pressure wave. When an object vibrates, it creates a mechanical disturbance in the medium in which it is directly adjacent to. Usually, the medium is air. The medium then carries the disturbance in the form of oscillating and propagating pressure waves.

The frequency of the waves are dependent on the frequency of the vibrating source. If the frequency of the vibrating source is high, then the sound wave will also have a high frequency. The sounds that we hear, from the voice of the person right next to you, to the music coming from your iPod earphones, to the crashing noise of shattered glass, all come from a vibrating source.

As the sound waves propagate through a medium, the pressure at a localized region in the medium alternates between compressions and rarefactions (or decompressions). Thus, if at one instant, a region in the medium experiences compression, the regions adjacent to it along the line of propagation are expected to be experiencing rarefactions.

Then as time progresses, the region in question undergoes a rarefaction while those adjacent to it undergo compressions. Therefore, if no medium exists, then the compressions and rarefactions cannot occur.

Now, how does one hear sounds? Remember how a source has to vibrate to produce a sound wave, and how a vibrating medium (e.g. air) has to exist to allow the sound wave to propagate? In the same manner, the receiver of the sound has to have something that can vibrate in order to ‘interpret’ the sound carried by the vibrating medium.

In the case of our ears, our eardrums serve as the receivers. When the vibrating air reaches our eardrums, it causes our eardrums to vibrate as well. The eardrums then transmit these vibrations to tiny bones in the middle ear, and so on until they reach the inner ear where the oscillating pressures are converted into electrical signals and sent to the brain.

Our ears are sensitive to vibrations between 20 to 20,000 Hz. Normally, frequencies that are higher or lower than the range provided cannot be processed by our auditory system. Young kids however, are able to hear slightly higher frequencies. That means, the range over which we are sensitive to diminishes as we grow older.

We have some articles in Universe Today that are related to sound. Here are two of them:

  • Hypersonic
  • Supersonic

Speed of sound references, brought to you by NASA. Here are the links:

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

Sources:
Indiana University
Wikipedia

Posted on by Tega Jessa

Oxygen Cycle

The oxygen cycle is the cycle that helps move oxygen through the three main regions of the Earth, the Atmosphere, the Biosphere, and the Lithosphere. The Atmosphere is of course the region of gases that lies above the Earth’s surface and it is one of the largest reservoirs of free oxygen on earth. The Biosphere is the sum of all the Earth’s ecosystems. This also has some free oxygen produced from photosynthesis and other life processes. The largest reservoir of oxygen is the lithosphere. Most of this oxygen is not on its own or free moving but part of chemical compounds such as silicates and oxides.

The atmosphere is actually the smallest source of oxygen on Earth comprising only 0.35% of the Earth’s total oxygen. The smallest comes from biospheres. The largest is as mentioned before in the Earth’s crust. The Oxygen cycle is how oxygen is fixed for freed in each of these major regions.

In the atmosphere Oxygen is freed by the process called photolysis. This is when high energy sunlight breaks apart oxygen bearing molecules to produce free oxygen. One of the most well known photolysis it the ozone cycle. O2 oxygen molecule is broken down to atomic oxygen by the ultra violet radiation of sunlight. This free oxygen then recombines with existing O2 molecules to make O3 or ozone. This cycle is important because it helps to shield the Earth from the majority of harmful ultra violet radiation turning it to harmless heat before it reaches the Earth’s surface.

In the biosphere the main cycles are respiration and photosynthesis. Respiration is when animals and humans breathe consuming oxygen to be used in metabolic process and exhaling carbon dioxide. Photosynthesis is the reverse of this process and is mainly done by plants and plankton.

The lithosphere mostly fixes oxygen in minerals such as silicates and oxides. Most of the time the process is automatic all it takes is a pure form of an element coming in contact with oxygen such as what happens when iron rusts. A portion of oxygen is freed by chemical weathering. When a oxygen bearing mineral is exposed to the elements a chemical reaction occurs that wears it down and in the process produces free oxygen.

These are the main oxygen cycles and each play an important role in helping to protect and maintain life on the Earth.

If you enjoyed this article there are several other articles on Universe Today that you will like. There is a great article on the Carbon Cycle. There is also an interesting piece on Earth’s atmosphere leaking into space.

There are also some great resources online. There is a diagram of the oxygen cycle with some explanations on the NYU website. You should also check out the powerpoint slide lecture on the oxygen cycle posted on the University of Colorado web site.

You should also check out Astronomy Cast. Episode 151 is about atmospheres.

Posted on by Jean Tate

Universe Puzzle No. 7

As with last week’s Universe Puzzle, something that cannot be answered by five minutes spent googling, a puzzle that requires you to cudgel your brains a bit, and do some lateral thinking. This is a puzzle on a “Universal” topic – astronomy and astronomers; space, satellites, missions, and astronauts; planets, moons, telescopes, and so on.

As this week’s puzzle may be a bit harder than most, I’ll be adding a HINT tomorrow, if it looks like no one is even close to being on the right track.

UPDATE: Answer has been posted below.

What do the following objects have in common?
NGC 6822, NGC 598, NGC 221, NGC 224, and NGC 5457.

Together with the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC), these are the seven galaxies (“nebulae”) with the most reliable distances, used by Edwin Hubble to establish the distance-redshift relationship, in his landmark 1929 paper. Today we call this the Hubble relationship.

“The data are given in table 1. The first seven distances are the most reliable, depending, except for M 32 the companion of M 31, upon extensive investigations of many stars involved.”

Hubble, Edwin, “A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae” (1929) Proceedings of the National Academy of Sciences of the United States of America, Volume 15, Issue 3, pp. 168-173

Note that not all are in the Local Group, and they are not the five brightest galaxies in Table 1. Figure 1 from that paper is reproduced in the Universe Puzzle graphic; it’s at the top right.

Well done Matthew Burns and iantresman!

Check back next week for another Universe Puzzle!