Astropulse
Astropulse
条目正在翻译，Astropulse 的相关介绍可以先看Astropulse: A Fresh Look at the Skies in Search of E.T.
Astropulse is a distributed computing project that uses volunteers across the globe to lend their unused computing power to search for primordial black holes, pulsars, and ETI. Volunteer resources are harnessed through Berkeley Open Infrastructure for Network Computing (BOINC) platform. In 1999, the Space Sciences Laboratory launched Seti@Home, which would rest on massively parallel computation on desktop computers scattered around the world. SETI@home utilizes recorded data from the Arecibo radio telescope and searches for narrow bandwidth radio signals from space, signifying the presence of extraterrestrial technology. It was soon recognized that this same data might be scoured for other signals of value to the astronomy and physics community.
Astropluse 是一个分布式项目，该项目利用全球志愿者他们的计算机闲置计算能力来寻找原始黑洞、脉冲星、和地位文明。志愿者的计算资源是通过 BOINC 平台来提供。在1999年，空间科学实验室启动了 SETI@home 项目，这将大规模的并行计算分散到世界各地的桌面计算机进行。SETI@home 利用从阿雷西博天文望远镜获得的数据来寻找太空中的窄带无线电信号，探索地外文明。很快的，这些分析的数据被认为可能是对天文学和物理社区的另外一种有价值的信号。
Development
For about 6 years, Astropulse existed in an experimental Beta testing phase not available to the general community. In July of 2008, Astropulse was integrated into SETI@home, so that the massive network of SETI participants could also contribute to the search for other astronomical signals of value. Astropulse also makes contributions to the search for ET. First, project proponents believe it may identify a different type of ET signal not identified by the original Seti@Home algorithm. Second, proponents believe it may create additional support for SETI by providing a second possible concrete result from the overall search project.
Astropulse searches for both single pulses and regularly repeating pulses. This experiment represents a new strategy for SETI, postulating microsecond timescale pulses as opposed to longer pulses or narrowband signals. They may also discover pulsars and exploding primordial black holes, both of which would emit brief wideband pulses. The primary purpose of the core Astropulse algorithm is coherent de-dispersion [1] of the microsecond radio pulses for which Astropulse is searching. Dispersion of a signal occurs as the pulse passes through the interstellar medium (ISM) plasma, because the high frequency radiation goes slightly faster than the lower frequency radiation. [2] Thus, the signal arrives at the radio-telescope dispersed depending upon the amount of ISM plasma between the Earth and the source of the pulse. Dedispersion is computationally intensive, thus lending itself to the distributed computing model.
Astropulse utilizes the distributed computing power of SETI@home, delegating computational sub-tasks to hundreds of thousands of volunteers' computers, to gain advantages in sensitivity and time resolution over previous surveys. Wideband pulses would be "chirped" by passage through the interstellar medium; that is, high frequencies would arrive earlier and lower frequencies would arrive later. Thus, for pulses with wideband frequency content, dispersion hints at a signal's extraterrestrial origin. It searches for pulses with dispersion measures ranging from 50 pc cm-3 to 800 pc cm-3 (chirp rates of 7000 Hz to 400 Hz per microsecond) allowing detection of sources almost anywhere within the Milky Way.
Final development of astropulse has been a two-part endeavor. The first step was to complete the astropulse C++ core that can identify successfully a target pulse. Upon completion of that program, the team created a trial dataset that contained a hidden pulse, which the completed program successfully found, thus confirming the ability of the astropulse C++ core to successfully identify target pulses.
The BOINC idea is to divide (split) large blocks of data into smaller units, each of which can be distributed to individual participating work stations. To this end, the project then began to embed the Astropulse C++ core into the Seti Beta client and began to distribute real data, split into astropulse work units, to a team of beta testers. The challenge has been to assure that the astropulse core will work seemlessly on a broad array of operating systems.
Project proponents believe that Astropulse will either detect exploding black holes, or establish a maximum rate of 5 x 10-14 pc-3 yr-1, a factor of 104 better than any previous survey. [3] The future of the project depends on extended funding to SETI@home.
Potential Pulse Finds
Primordial Black Holes
"According to the Big Bang Model (also called the Standard Model), during the first few moments after the Big Bang, pressure and temperature were extremely great. Under these conditions, simple fluctuations in the density of matter may have resulted in local regions dense enough to create black holes. Although most regions of high density would be quickly dispersed by the expansion of the universe, a primordial black hole would be stable, persisting to the present." Wikipedia Primordial Black Holes One goal of Astropulse is to detect postulated mini black holes that might be evaporating due to "Hawking radiation". Such mini black holes [4] are postulated to have been created during the big bang, unlike currently known black holes. Martin Rees has theorized that a black hole, exploding via Hawking radiation, might produce a signal that's detectable in the radio. The Astropulse project hopes that this evaporation would produce radio waves that Astropulse can detect. "The evaporation wouldn't create radio waves directly. Instead, it would create an expanding fireball of high energy gamma rays and particles. This fireball would interact with the surrounding magnetic field, pushing it out and generating radio waves."
RRAT's
Rotating radio transients (RRATs) are a type of neutron stars discovered in 2006 by a team led by Maura McLaughlin from the Jodrell Bank Observatory at the University of Manchester in the UK. RRAT's are believed to produce radio emissions which are are very difficult to locate, because of their transient nature. [6] Early efforts have been able to detecting radio emissions, sometimes called an RRAT flash, [7], for less than one second a day, and like other single burst signals, one must take great care to distinguish them from terrestrial radio interference. Distributing computing and the astropulse algorithm may thus lend itself to further detection of RRAT's.
Extragalactic Pulses
D. R. Lorimer and others analyzed archival survey data and found a 30-jansky dispersed burst, less than 5 milliseconds in duration, located 3° from the Small Magellanic Cloud. They reported that the burst properties argue against a physical association with our Galaxy or the Small Magellanic Cloud. In a recent paper, they argue that current models for the free electron content in the universe imply that the burst is less than 1 gigaparsec distant. The fact that no further bursts were seen in 90 hours of additional observations implies that it was a singular event such as a supernova or coalescence of relativistic objects. [8] It is suggested that Hundreds of similar events could occur every day and, if detected, could serve as cosmological probes. Radio pulsar surveys such as Astropulse-Seti@Home offer one of the few opportunities to monitor the radio sky for impulsive burst-like events with millisecond durations. [9]. Because of the isolated nature of the observed phenomenon, the nature of the source remains speculative. Possibilities include a black hole-neutron star collision, a neutron star-neutron star collision, a black hole-black hole collision, or some phenomenon not yet considered.
ET
Previous searches by Seti@Home have looked for extraterrestrial communications in the form of narrow-band signals, analogous to our own radio stations. The Astropulse project argues that since we know nothing about how ET might communicate, this might be a bit closed-minded. Thus, the Astropulse survey can be viewed as supplementing the narrow-band Seti@Home survey as a bi-product of the search for physical phenomena.
Undiscovered Phenomena
Radio astronomers have made some exciting discoveries. RF radiation from outer space was first discovered by Karl G. Jansky (1905-1950) who worked as a radio engineer at the Bell Telephone Laboratories to studying radio frequency interference from thunderstorms for Bell Laboratories. He found “ . . . a steady hiss type static of unknown origin,” which eventually he concluded had an extraterrestrial origin. Pulsars (rotating neutron stars) and quasars (dense central cores of extremely distant galaxies) were both discovered by radio astronomers. In 2003 astronomers using the Parkes radio telescope discovered two pulsars orbiting each other, the first such system known. Explaining their recent discovery of a powerful bursting radio source,[10] NRL astronomer Dr. Joseph Lazio stated, “Amazingly, even though the sky is known to be full of transient objects emitting at X- and gamma-ray wavelengths, very little has been done to look for radio bursts, which are often easier for astronomical objects to produce.” The use of coherent dedispersion algorithms and the computing power provided by the SETI network may lead to discovery of previously undiscovered phenomena.
Astronomy in the Schools
Astropulse and its older partner, SETI@Home, offers a concrete way for secondary school science teachers to involve their students with astronomy and computing in a concrete way. A number of schools maintain distributed computing class projects.