Jika anda ternampak muka saya tengah TT (Teh Tarik) ni, bermakna anda telah selamat mengharungi 3 hari bumi tak jadi bergelap, dan tarikh 21hb Dis yang penuh tragis dan huru-hara (kononlah).
Nak ceritanya, Falak Online telah pun berpindah rumah. Bermula sekarang silalah kemaskini link ke WWW.FALAKONLINE.NET , tak perlulah letak apa-apa selepas tu, kerana ia akan redirect ke muka hadapan BARU yang sepatutnya.
Laman lama (yang anda lihat sekarang ni), InsyaAllah akan kekal untuk beberapa bulan mendatang. Ia akan menyenaraikan KESEMUA artikel lama saya di FO, bagi rujukan anda semua. Maka, kalau anda nak masih nak marah-marah kat saya berkenaan artikel "3 hari bergelap tu" , masih boleh berbuat demikian, saya terima dengan hati terbuka! :-)
Apa pun, InsyaAllah 2013 mendatang akan terdapat beberapa pembaharuan yang saya dan rakan-rakan Personaliti Astronomi lain usahakan, demi kemajuan bidang Astronomi di Malaysia.
Jom dan Selamat Datang Ke Tahun Baru 2013.
Jemput masuk ---> WWW.FALAKONLINE.NET
Evidence from observations sheds doubt on cosmic cannibalism as a source for galaxy growth, suggesting that instead galaxies grow by pulling in gas from the intergalactic medium.
A quick stroll through Hubble’s archive shows a surplus of massive spiral galaxies — a tapestry of the drama of stellar birth and death across thousands of light-years. But one question remains: how do these galaxies continue forming stars at such a fast clip?
Galaxies should quickly deplete their reservoirs of gas as they create new stars and so must somehow continuously replenish those reservoirs with fresh gas to keep the star formation going.
Last year, a series of studies showed that galaxies power most of their star formation — and therefore their growth — through merging with dwarf companions. The Milky Way is a prime example, as it shows no signs of a major merger, but continuously munches on nearby dwarf galaxies.
But a new study shows this might not be the case.Minor Mergers are Minor Players
Enrico Di Teodoro (University of Bologna, Italy) and his colleagues set out to better understand this process by observing 148 spiral galaxies and any companion dwarfs they may soon accrete.
But the results were surprising: of the 148 galaxies in their sample, 101 had no detectable companions, 15 showed a massive companion, 6 showed both massive and dwarf companions, and 26 showed only dwarf companions.
So the team focused on the 32 galaxies with dwarf companions, finding that any future mergers would only provide the massive spiral galaxy with 0.28 solar masses per year of gas — approximately a fifth of the gas necessary to continue forming stars (1.29 solar masses per year).
In other words, the number of dwarf galaxies is simply too low to supply enough gas to each massive galaxy.
A reader in the know might recall the missing satellites problem — the discrepancy between the number of small, faint galaxies predicted to exist in numerical simulations and the number actually seen. Are there extremely faint galaxies that Di Teodoro and his colleagues couldn’t see, potentially biasing their result?
“The missing satellites problem arises from numerical simulations that likely are not yet able to reproduce the whole physics,” says Di Teodoro. “Very deep observations in the Local Group show no evidence of a significant population of very low-mass dwarf galaxies as predicted by simulations. Personally, I believe that the lack is in the current simulations rather than in the observations.”
Nonetheless the team calculated the contribution given by any dwarf galaxies that were too faint to be observed. They found the contribution to be negligible.Intergalactic Gas Feeds Galaxies
So the team has reopened the question: how do these galaxies grow?
“The question of how spiral galaxies can continue to form stars at a nearly steady state is still open, and the picture seems to be much more complicated than people used to think a few years ago,” says Di Teodoro.
One option is that galaxies grow by pulling in gas from the intergalactic medium — the hot plasma found between galaxies. But only cold gas is the fuel for star formation. At low temperatures, atoms within the gas are able to bind together and also clump to high densities. So in order for this scenario to work, the gas would need to cool down, a process that has proved difficult to observe directly, says Di Teodoro.
Two experts, Sugata Kaviraj (University of Hertfordshire and University of Oxford, U.K.) and Diego Lambas (University of Córdoba) find the study presented here statistically sound.
“At the present, gas accretion from satellites does not provide a major contribution to the star formation rate of spirals,” affirms Lambas. He does, however, caution that minor mergers will not have a negligible effect: star formation is a natural consequence of a tidal interaction. As the massive spiral galaxy engulfs the dwarf galaxy, any gas within will feel a headwind, much as a runner feels a wind even on the stillest day, and become compressed enough to spark star formation.
“Minor mergers do not just bring gas into massive spiral galaxies,” says Kaviraj. “The infall of satellites can disturb the existing gas in the spiral itself and induce radial inflows which then produce star formation. Hence the satellites can ‘trigger’ star formation from the gas that is already in the massive spiral itself.”
It’s possible that the impact of the dwarf galaxy mixing up the gas in the spiral is larger than the impact from gas injected into the spiral, says Kaviraj. The issue will have to be explored further before astronomers can determine the true culprit behind continued star formation in massive spiral galaxies.
Enrico Di Teodoro and Filippo Fraternali “Gas Accretion from Minor Mergers in Local Spiral Galaxies” Astronomy & Astrophysics, June 5, 2014
This month's usually dependable Perseid meteor shower competes with a nearly full Moon. If you can find a dark viewing location, you might see a bright meteor every few minutes when the shower peaks on the night of August 12–13.
Every three years the Moon displays similar phases at the same dates on the calendar. The rule of thumb is that every phase happens just three days earlier than it did three years ago, on average. You might recall that in 2011 the Perseid meteor shower contended with an almost-full Moon.
Well, it's happening again.
This time the Moon will be two days past full on the peak Perseid night, August 12–13. So it won't be quite as bright as when it's full, but it will illuminate the sky all night, especially from midnight to dawn when the shower's radiant in Perseus is high and the meteors should be most numerous.
But at nightfall the Moon will still be low in the east, and this is when to watch for Earthgrazing Perseids. These are the infrequent, but unusually long and graceful, meteors that you may see when a shower's radiant is low above the horizon.
On their peak night, the Perseids typically produce about 100 meteors per hour when the radiant is near the zenith (directly overhead) and the sky is very dark. The peak rate typically runs for about 12 hours centered on the predicted time, which this year is 0h Universal Time on August 13th (near nightfall on August 12th in North American time zones).
Moonlight will hide faint Perseid meteors, but a nice bright one might show through every few minutes late in the night.
But don't limit yourself to the night of the peak. The shower stays above half of its maximum strength for two days running, and you may see a few Perseids as early the end of July and as late as August 18th, as shown in last year's activity graph at right. The drop-off happens faster than the rise — but the window of Moon-free darkness gets longer on the days following the peak.
Next year's peak Perseid nights will be moonless and ideal.
These meteors occur when bits of debris shed by Comet 109P/Swift-Tuttle slam into Earth's upper atmosphere at a relatively fast 37 miles (60 km) per second. The result is a trail of white-hot plasma (ionized air molecules) along each particle's path, and it's this column of plasma that creates the momentary streaks of light we see in the sky.
Attentive skywatchers realized in the 1830s that the Perseid meteor shower occurs during mid-August each year, though folklore suggests that its annual apparition was known long beforehand. Comet Swift-Tuttle, the shower's source, wasn't discovered until 1862.Meteor Watching: Fun for All
Meteor watching has become much more of a public thing than it used to be. News media promote the main annual showers in a way that never happened a generation ago. We're proud to have played a part in this; the grand Leonid displays from 1999 to 2002 certainly helped.
But we underestimated how modest a success it takes to get people hooked. Most people know better now that to expect fireworks. Vacationing families with no astronomy experience are often thrilled to see just two or three shooting stars on Perseid night, and many have made it a family tradition.
Remember: you need no equipment — or even knowledge of the constellations — to enjoy the show. Just bring a reclining chair to a dark spot with a wide-open view of the sky, face whatever direction is darkest, lie back, and watch the stars overhead.
Get great tips for watching and studying meteors with Sky & Telescope's ebook, Shooting Stars. It's a free download!
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Software Bisque announces its long-anticipated expansion into the app market with the release of TheSky Mobile ($14.99) for the iPhone and TheSky HD for the iPad ($29.99). Both include an extensive feature set tailored to the intermediate and advanced amateur. TheSky for iOS integrates popular features from the desktop editions, including field-of-view indicators for many telescope, eyepiece, and camera combinations; large astronomical databases (including satellites and minor planets); integrated photos of popular astronomical objects; and much more. TheSky’s Wi-Fi telescope control (a Wi-Fi-to-serial adapter is required and sold separately) offers a powerful and elegant alternative to your Go To telescope’s hand paddle, allowing you to control their telescopes directly with your iPhone or iPad device. TheSky HD for the iPad also integrates with DC-3 Dreams ACP Observatory Control Software, enabling users to plan, submit to ACP, and execute their observing session without having to exit TheSky. Additional catalog plug-ins can be downloaded from the manufacturers website free of charge.
SkyandTelescope.com's New Product Showcase is a reader service featuring innovative equipment and software of interest to amateur astronomers. The descriptions are based largely on information supplied by the manufacturers or distributors. Sky & Telescope assumes no responsibility for the accuracy of vendors statements. For further information contact the manufacturer or distributor. Announcements should be sent to nps@SkyandTelescope.com. Not all announcements will be listed.
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