The Milky Way's black hole may spring to life in 2013

By John Timmer | Published December 14, 2011 1:59 PM

The Milky Way's black hole may spring to life in 2013
The gas cloud's path (red) takes it past many of the stars that orbit our galaxy's central black hole.

Quasars, the brightest objects we're aware of, are powered by the supermassive black holes that are thought to reside at the center of every galaxy. But many galaxies fail to feed their black holes enough matter, leading to a body that's quiet and difficult to detect. Our own galaxy's central black hole, called Sgr A*, falls into the latter category. We can detect it at wavelengths up to the X-ray range, but it's dim enough that we'd have a hard time spotting it if it weren't so close.

That may be about to change, however. Astronomers have spotted a cloud of gas with a mass about three times that of Earth that's on a trajectory that will have it pass close to Sgr A* in 2013. When it does, it may feed matter into the black hole's accretion disk, powering a sudden surge in Sgr A*'s output.

Since Sgr A* doesn't emit much in the way of radiation, a lot of what we've learned about it comes from tracking the stars that orbit it at close range; many of these have eccentric orbits that take them very close to the black hole. The Very Large Telescope has a program set up to perform periodic observations of the stars in order to track their orbits closely. It was during these observations that the team "discovered an object moving at about 1,700 km/s along a trajectory almost straight towards Sgr A*."

Observations of its emissions indicated that the object was a gas cloud that was much more dense than the material that's typically found in the area, and cooler as well. It's not quite heading straight at Sgr A*, but it's on a highly eccentric orbit that will take it extremely close to the body—36 light hours by the summer of 2013 (for comparison, the Voyager spacecraft are over a dozen light hours from the Earth). As a result of this plunge, the black hole's gravity has been accelerating the gas within the time we've been observing it; its total velocity (including some motion that's not towards the black hole) has increased from 1,200 km/s to nearly double that speed over the last seven years.

In the nearly 20 years we've been observing Sgr A*, only two stars have ever come closer to it. But stars are held together by gravity; this cloud is too diffuse to have that sort of coherence. As a result, the authors expect that it will undergo dramatic changes as it blasts in to the neighborhood of the black hole. The shock of hitting the low-density, high-temperature gas will compress the cloud even as the black hole's gravity starts to stretch it out along the direction of its orbit. This could eventually split the cloud into multiple fragments, each of which may take a slightly different path around the black hole.

As these fragments reach the point in the orbit closest to black hole, its temperatures may reach 106K, hot enough for it to start emitting X-rays.

But that may not be the only fireworks. If the cloud does end up fragmenting, then there's a chance that one of the fragments will end up feeding into the accretion disk surrounding the black hole. "This could in principle release up to around 1048 erg over the next decade," the authors estimate. We'll have to wait and see, but you can be sure lots of electronic eyes will be watching.

In the meantime, when nothing in particular happens in 2012, the cloud's destruction may end up providing a new bit of excitement for doomsday aficionados.

Nature, 2011. DOI: 10.1038/nature10652  (About DOIs).

Photograph by ESA
 
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The Ars Technica 2011 Child's Play Drive has raised over $17,000! Let's keep it going

The Ars Technica 2011 Child's Play Drive has raised over $17,000! Let's keep it going

We've been running our own Child's Play drive this time of the year for the past few years, and it has long been one of my favorite projects. We set this year's first goal at $10,000 when we launched the drive, and we've smashed that goal pretty handily: we're proud to announce our total rests at $17,531 raised from readers of Ars Technica.

I can't say rests, actually, because donations continue to come in, and keeping track of how many people are donating and keeping a record of our total is a large part of my day right now. Can you imagine what it's like to wade through piles of e-mails that prove the generosity of people? It's like grunt work that feeds your soul. If you head over to the official Child's Play site, you'll also see the Ars Technica logo under the Platinum Sponsors section, and we're in some wonderful company there. You guys made that happen.

Last year we raised a little over $24,000 for the charity, and I'd like to beat that total this year. We're already doing much better than I had hoped, and I think we can do it, no sweat. If you think a $2 donation is silly, don't. If you think it's not worth your time to donate $20, let me tell you that your donation is going to be put with thousands of other people that donated smaller amounts, and it's going to buy piles of video games, books, and toys. The kids don't care if you only paid for half of an item, they're just going to know their holidays are a little better because someone decided to give.

Are you ready? Let's smash that goal.

Why should I donate? How do I donate?

The "why" is simple: by placing a monetary donation (or by buying items directly), you're making sure children who are stuck in the hospital for the holidays have toys, books, and video games to play with. Gaming can take players far away from their actual surroundings, and that's never more important than when your reality is a long-term stay in a medical facility.

Donating couldn't be easier. Simply go to the official Child's Play page and donate via Paypal, or click on one of the individual hospitals to view its Amazon wishlist and purchase those items directly. You can also text GAMERS to 50555 to donate $5 instantly. Between Paypal, Amazon, and text messaging, everyone has an easy way to donate, and every little bit helps.

Now, here's the fun part. Grab a digital copy of your receipt (it can be a screenshot or simply a cut and paste of the text) and send it to ChildsPlay@arstechnica.com. Your receipt gets you an entry into our drawing for the prizes you'll read about below. (One entry per person, see official rules for entry without purchase) We'll choose 17 winners on January 10, 2012, and those winners get to choose their prize packages (choosing takes place in the order that the winners were drawn). Donations need to be made before January 4th to be eligible for the prizes. Here are the full rules.

Also, be sure to check our first post to look at the prizes we're offering! This isn't nearly as fun unless we offer some interesting and one-of-a-kind gaming items to give away.

Photo illustration by Aurich Lawson
 
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Can a $100 iPad case improve 3G data power?

Can a $100 iPad case improve 3G data power?
Pong's iPad 3G case folds like origami to provide the tablet with a convenient kickstand

Were I to tell my most perpetually indignant friend that his tablet's 3G radio is prone to regular performance drops of up to 75 percent, he would likely enter apoplectic rage.

Such is the emotional fabric of the modern tech enthusiast. We're already concerned about overloaded data networks that can't handle too many simultaneous user requests, and Apple's iPhone 4 "antennagate" imbroglio, rightly or wrongly, has left conspiracy-minded consumers wary of self-sabotaging hardware.

But now a company called Pong Research is spreading word of a proximity sensor inside the iPad 2 WiFi + 3G that reduces the tablet's 3G radio output by some 6 dBm, or about three-quarters of its total transmission strength. The sensor is tripped whenever it comes within 10mm of a solid object—which could be anything from human flesh to an iPad case that snugly ensconces the tablet's chassis.

Apple doesn't mention the proximity sensor in any of its marketing materials or user manuals, and it declined to comment for this article. But the sensor is referenced in Apple's filings with the FCC, which make frequent reference to a 3G radio "back-off" mode.

So what is Pong's stake in the game? The company specializes in third-party iPhone and iPad cases marketed as providing consumers with additional protection from the electromagnetic radiation emitted by their devices. As a side benefit, Pong's iPad 3G case purportedly doesn't trip the proximity sensor. Other third-party cases, Pong says, trip the sensor and leave the user with reduced 3G power.          

To validate Pong's claims, I visited Cetecom Inc., an FCC compliance lab, and observed while technicians tested the iPad 3G case under the full scrutiny of scientific inquiry. But before I reveal the test results, let's dig a little deeper into the iPad's proximity sensor. Why did Apple include a potential data governor in the 3G version of its tablet, and what effect does its back-off mode really have on real-world 3G data connections?

Down the FCC rabbit hole

Unless you burrow your way into a cryptic database of public FCC filings, it's near impossible to find any evidence of an iPad proximity sensor. Indeed, simple Google searches only reveal speculation about the features a proximity sensor might provide were one to be deployed in Apple's tablet. One thread of what-if-ing from January posits an auto-unlocking function that would be triggered as soon as a user picks up the device.

But evidence of the proximity sensor can indeed be found in a report prepared for Apple by Compliance Certifications Services (CCS), and submitted to the FCC on March 1, 2011. Titled "SAR Evaluation Report," the document chronicles a series of tests to determine how much electromagnetic radiation a user might absorb from the iPad's wireless communications hardware. SAR stands for "specific absorption rate," and is the metric by which the FCC measures radiation exposure to the human body.

Deep inside the report, CCS makes note of the iPad's proximity sensor in a section titled "Power Reduction By Sensing." In summary, when the proximity sensor comes within 10mm of a solid object, it triggers a "back-off" mode that reduces the power of the iPad's 3G radio (which, along with the sensor itself, resides to the right of the front-facing camera in the iPad 2 WiFi + 3G). CCS ran a series of tests to determine not only the degree of power reduction across various radio bands, but the effect of power reduction on SAR.

This diagram from an FCC filing indicates the location of the iPad's proximity sensor.
This diagram from an FCC filing indicates the location of the iPad's proximity sensor.

While Apple wouldn't comment on the sensor, it's easy to glean the sensor's intent from both its cause-and-effect properties, and the fact it plays such a big part in a report on radiation absorption.

"It looks like the sensor is looking for human tissue next to the antenna, and if it sees it, it backs off the transmit power," says Francis Sideco, iSuppli's senior principal analyst for wireless communications. "You would assume that the FCC had some kind of requirements that the iPad had to meet."

Like iSuppli's senior wireless expert, even the teardown mavens at iFixit were unaware of the proximity sensor before I showed them FCC documentation. But in typically intrepid iFixit fashion, they got right down to business, and unearthed what they suspect could be the physical component itself.

Says iFixit's Miro Djuric: "The only component that I could see that could possibly be the proximity sensor is a teeny tiny component that's attached to the black plastic bar contained in the 3G version. That component is completely missing from the WiFi version, which allows us to conclude that the WiFi version doesn't need it."

Thanks to iFixit, we have visual evidence of what might be the proximity sensor in question. The iPad on the top is WiFi only. Below we see the 3G version of the same tablet
Photograph by Ariel Zambelich/Wired.com

And why did Apple put the sensor in the iPad?

Djuric posits: "It's to limit the amount of SAR exposure a user would get, should they place themselves next to the iPad while it's transmitting information—for example, falling asleep on top of the iPad while watching a lame movie on Netflix. The impact of radiation decreases dramatically with distance, so you're a lot safer with your iPad six inches from your head than you are with it pressed right up to your face."

While the SAR Evaluation Report from CCS makes frequent reference to the proximity sensor, it doesn't describe its operation or even intent. For this information, readers are directed to a separate document titled "Operational Description"—a report that's been tagged "Permanent Confidential" by the FCC, and is unavailable for public review.

Pong's secret weapon: radiation redistribution

So we know the proximity sensor exists, and that it attenuates 3G radio power. Our line of inquiry now turns to Pong Research, and its marketing claims.

Pong makes two promises about its case: First, that its case won't trigger the proximity sensor, while competing cases will. "The proximity sensor is triggered not just by the human body, but by any solid. As a result, all commercial cases for the iPad 2 also cause the proximity sensor to trigger, which can reduce your transmission power by up to 75 percent," the company writes.

Pong's case design redistributes energy across a larger surface area, reducing the radiation hotspot over the 3G radio.

The company's sensor solution is fairly straightforward: Its case has a cut-out over the part of the iPad where the proximity sensor is located—a strategy that can be employed by any case manufacturer that knows about the sensor, and is concerned about the tablet's back-off mode.

Pong's second promise is more ambitious. It says its case includes an integrated circuit board designed to "couple passively" with the tablet's own 3G antenna, and redistribute 3G radiation away from the user's body.

"Normally, the radiation from the iPad is concentrated near the antenna," says Ryan McCaughey, the Chief Technology Officer at Pong Research. "The Pong case redistributes the 3G radiation over a larger area to reduce the intensity and lower SAR. It's a passive device, and doesn't amplify the signal."

This is a completely separate matter from the proximity sensor, and it's Pong's raison d'être. As as a safety measure, FCC regulations limit SAR levels for partial-body exposure to up to 1.6 W/kg (watts/kilogram), and whole body exposure to up to 0.08 W/kg. But Pong caters to consumers who worry that even FCC-approved levels of radiation might have long-term health implications. Pong's phone cases, and now their iPad cases, promise extra protection by redistributing radiation away from the consumer's body.

Bold claims. How would they hold up in Cetecom's lab?

Testing the body phantom

Located in the business park sprawl of Milpitas, Califorinia, Cetecom Inc. is easy to miss, with a nondescript, near-featureless exterior. But walk down its hallways, and you'll discover the company is home to hardcore testing chambers filled with massive robotic arms, gigantic wall-mounted turntables, and sensitive electronics equipment calibrated to the nth degree. Cetecom is a major player in FCC compliance testing, and graciously agreed to help us validate Pong's claims.

Our first series of tests delved into SAR—specific absorption rate, or, in lay terms, how much radiation one's body may receive from handling the iPad WiFi + 3G. We first ran the test with the iPad alone, sans case, and then repeated the regimen with the Pong case attached. According to Pong, its case should reduce SAR by about two-thirds.

The SAR testing apparatus in an impressive set-up. The device under review is carefully positioned below a basin filled with a special liquid solution called a "body phantom." The phantom is mostly water with a small amount of ethanol, and simulates the electrical properties of body tissue.

A huge robotic arm controls the SAR probe as it penetrates the body phantom

Above the basin moves a probe controlled by an industrial-strength robotic arm. The probe enters the phantom, and does a precise area scan, searching for electromagnetic hotspots where the iPad is radiating the most. Once identified, hotspots are investigated further with a more penetrating volume scan, which ultimately yields the SAR numbers supplied to the FCC.

Our results? The Pong case delivered all the radiation protection it advertises.

Before we ran the tests, the company provided me with documents from its own SAR testing. On the 1880MHz WCDMA 3G radio band, Pong's paperwork shows that a "naked" iPad emits an average SAR of 1.44 mW/g (milliwatts per gram), while an iPad with Pong's case attached lowers SAR to 0.445 mW/g.

At Cetecom, we tested the very same radio band, and observed that same two-thirds reduction in SAR. (Per an agreement with Cetecom, I won't be sharing specific numbers from the tests I observed in their lab.)

In total, it's an impressive product for anyone concerned about receiving excessive amounts of radiation while holding an iPad in the throes of 3G transmission. (We found the same results when we tested Pong's iPhone case in 2009.)

So that's SAR. What about Pong's claims that its case doesn't trip the proximity sensor, unlike other third-party cases?

Inside the anechoic chamber

To test the power of the iPad's 3G radio—and to determine what really happens when the proximity sensor is tripped—we entered Cetecom's over-the-air testing facility. Testing apparatus is spread across two rooms: an anechoic chamber covered top to bottom with foam pyramids that absorb stray radio waves, and an external room filled with equipment that measures the procedures occurring inside the chamber itself.

Inside the anechoic chamber, we placed the iPad 2 on a pedestal that rotates 360 degrees. On the wall of the chamber is a massive turntable with a 3G antenna attached. To build a 3D model of the iPad 2's 3G transmission strength, the pedestal rotates in a circle while the turntable-mounted antenna sweeps across a 165-degree arc across an opposing axis. The antenna measures 3G signal strength at specific points on the arc, and reports back to the testing equipment in the other room.

Looking like something from the game Portal 2, the anechoic chamber is filled with RF-absorbing pyramids and a gigantic wall-mounted turntabl
Looking like something from the game Portal 2, the anechoic chamber is filled with RF-absorbing pyramids and a gigantic wall-mounted turntabl

We ran three tests: the iPad 2 transmitting "naked," the tablet transmitting while seated in the Pong case, and the tablet transmitting while seated in another third-party case that firmly grips the entire bottom and sides of the iPad's chassis.

Our results at Cetecom perfectly mapped against the numbers CCI provided in its SAR Evaluation Report filed with the FCC. In this report, CCI indicates average 3G power drops from 22.4 dBm to 16.4 dBm when the proximity sensor back-off is triggered.

Just as Pong promised, we saw this 6 dBm reduction in our own testing: The iPad transmitted at full power when running naked and when seated in the Pong case, but its power attenuated when seated in the other third-party case. Because the dBm scale is logarithmic and not linear, this seemingly small reduction in power actually represents a power drop in the neighborhood of 75 percent.

But what does a 75 percent reduction really mean to users tapping into 3G in the field?

If you're currently using a third-party iPad 2 case that trips the tablet's proximity sensor, you really only need to be concerned about the tablet's ability to connect to faraway cell towers. According to McCaughey, Pong's CTO, "Reducing a phone or tablet's 3G signal strength will decrease the range within which the device can connect to a tower. A 75 percent reduction in transmission power, for example, produces a 50 percent smaller connectivity range."

Sideco, iSuppli's wireless expert, adds a bit more texture. He points out that out the tablet's radio strength affects the 3G uplink, and not the downlink, which is most central to the consumer experience—i.e., we typically download much more data than we ever upload.

Nonetheless, says Sideco, "The power back-off could impact acknowledgements by the application or the device going back to a server or base station. Therefore, you definitely want to optimize your power to balance what is needed or available versus its impact on battery life."

Sideco also points out that a 6 dBm drop might never be noticed by the user. "If the RF conditions are very clean, and you are also close to the tower, you might not even need anywhere near 16dB of power," he says. "The reduction only really comes into play in the boundary conditions where maximum transmission power is required."

So, in the final analysis, what are we to make of Pong's unique case design?

It's a very expensive accessory at $100, but it's made of a durable Lexan material that's soft to the touch, and looks nearly as smart as leather. This isn't a gaudy case. It reeks of purpose-built seriousness befitting Pong's intentions. And the case not only seats the iPad 2 with a firm grip, it also includes a unique folding cover that can be be arranged in a variety of stand configurations.

But when push comes to shove, you wouldn't spend $100 for aesthetics and a clever kickstand. You would buy the Pong case because you're concerned about radiation exposure, and want to ensure you're getting every bit of 3G power your iPad can muster.

To this end, the Pong case clearly, unequivocally delivers on both counts.

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Naked mole rats feel no pain due to acid

Naked mole rats feel no pain due to acid

African naked mole rats never cease to amaze. Not only are they exceedingly ugly, but they are the longest living rodents. Moreover, none have ever been observed to get cancer. And they are the only known vertebrates that are not bothered by acid. A report in this week's Science explains the molecular basis underlying this acid insensitivity, and suggests that it might be an adaptation to their oxygen-poor living conditions..

Acid causes pain by activating nociceptors, proton-triggered ion channels that activate neurons. This recent study compared acid receptors from naked mole rats and mice, and found that they were not all that different. Similar numbers of each receptor were found in the respective animals, and acid evoked similar levels of current through them.

Voltage gated sodium channels, which function in the propagation of nerve signals, are known to be inhibited by protons. It turns out that voltage-gated currents in the naked mole rat are much more susceptible to acid inhibition than those in mice. At pH6.0, the naked mole rat neurons exhibited a 63 percent reduction in conductance, which was significantly greater than the 42 percent reduction observed in the mouse neurons. 

Mild acidification shuts down both mouse and naked mole rat channels, preventing them from opening when confronted with a much lower pH. But this inactivation happens much faster in the naked mole rat.

How and why does acid inhibit naked mole rat nociceptors so potently? The threshold for triggering a nerve impulse by nociceptors is determined by a specific sodium gated channel. In humans, genetic mutations disabling the gene encoding this channel lead to complete insensitivity to pain, whereas activating mutations cause extreme pain disorders. 

Within the pore of this channel, there is a string of positively charged amino acids that controls acid sensitivity. In naked mole rats, these are replaced by negatively charged amino acids. The amino acid changes in the naked mole rat cause an increased proton sensitivity in their sodium channel, providing an inhibition too strong for acid to overcome. Thus acid cannot evoke nociceptor firing like it can in other animals.

Naked mole rats live in large colonies in underground burrows, which incidentally is why they are naked—they don't need any fur. But their subterranean environment is very high in CO2, which can lower the pH of tissues. 

There is also a species of microbat that lives in small caves and is therefore also subjected to a high CO2 environment. Its sodium channel has a negatively charged motif in it like the naked mole rat's, instead of a positively charged one like ours. Convergent evolution thus may have selected for these genetic variants to reduce acid sensitivity in these very different species that share similar extreme living conditions.

Science, 2011. DOI: 10.1126/science.1213760  (About DOIs).

Photograph by nsf.gov
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Week in gaming: Bioshock Infinite goes spiritual, Nerf review, RAAM's Shadow

Week in gaming: <em>Bioshock Infinite</em> goes spiritual, Nerf review, <em>RAAM's Shadow</em>

This was a great week for interesting stories, including a review of an impressively small but powerful Nerf gun and thoughts on the lyrics of a hymn used in the latest Bioshock Infinite trailer. We also revisited our Child's Play drive, with some impressive results. Come inside and see what you might have missed.

Oh, Lord: Ken Levine didn't remove religious lyrics from Bioshock Infinite trailer: The new trailer for Bioshock Infinite is beautiful, but some are taking offense to a change made to a beloved, and religious, American song. The truth is much simpler: the song used is accurate to the time period of the game, and no lyrics were changed.

The "best" of the VGAs: new Mass Effect 3, Bioshock Infinite trailers, and Tony Hawk HD: While the Video Game Awards may be painful to watch, the actual trailers and news that come out of the show are always exciting. Come inside and take a look at some of the games we're looking forward to—without the hateful awards show wrapped around them!

The latest Humble Bundle offers amazing games, promotes multiplatform releases: The latest Humble Bundle may offer the best series of games yet, including both Super Meat Boy, and Shank, and the "Bundle Advocate" hints at what's coming in the future for the Humble team.

The Nerf Jolt EX-1 is small, concealable, accurate, and it stings a little : The newest Nerf gun goes simple, small, and satisfying. This gun may look tiny, even cute, but its range and power are nothing to laugh at.

RAAM's Shadow DLC adds context, richness to world of Gears of Wars: RAAM's Shadow, a $15 content pack for Gears of War 3, shows what Sera looked like before the war destroyed much of the planet's elegance, and it puts you in control of one of the most powerful characters in the series.

Judge dismisses "Other OS" class-action suit against Sony: A class-action lawsuit against Sony for removing the "Other OS" features of the PlayStation 3 has been dismissed. The Judge noted that while the move may not have been the best thing for customers, there was no legal argument against Sony's actions in the current suit.

Free, high-quality updates are the key to Jetpack Joyride's success: Jetpack Joyride is an amazing game, but the quality and number of its free updates made us wonder about the business model. According to Halfbrick Studios, this approach requires a light touch, but the rewards can be great.

The Ars Technica 2011 Child's Play Drive has raised over $17,000! Let's keep it going: Our 2011 Child's Play drive has smashed our initial goal, so it's time to go after last year's total. Come inside to see where we're at, and where we need to be. This has been a great year already, so let's continue to make it better.

Real Big Shootin' add-on for the Gunstringer lets you live gaming's greatest fantasy: The Real Big Shootin' DLC package for the Gunstringer is only $3, offers limited gameplay, but the novelty of the shooting galleries and the fun of the "final boss" make it worth your time and money.

 
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