Mengenal Prof. Subrahmanyan Chandrasekhar

Chandrasekhar Fisikawan Ahli Bahasa 

Subramanyan Chandrasekhar, peraih nobel Fisika tahun 1983 dilahirkan di Lahore, India pada 19 Oktober 1910. Ayahnya, Chandrasekhara Subrahmanyan Ayyar adalah pegawai di departemen keuangan India. Sementara Ibunya, Sita (neé Balakrishnan) seorang ibu rumah tangga biasa namun berintelektual tinggi (ia mampu menerjemahan karya Henrik Ibsen, “A Doll House” ke bahasa Tamil). 

Kedua orangtuanya, menurut Chandrasekhar sangat menaruh perhatian pada pendidikan anak-anaknya. Orangtuanyalah yang langsung memberikan pendidikan dasar khusus baginya di rumah hingga ia berusia 12 tahun. 

Mereka mengharapkan Chandrasekhar terkenal seperti pamannya, Chandrasekhara V. Raman, orang India pertama yang meraih hadiah Nobel fisika. Pada tahun 1918, ayahnya dipindah tugaskan ke Madras dan di sanalah keluarganya kemudian hidup menetap.

Di Madras, ia bersekolah di sekolah lanjutan Hindu dari 1922 hingga 1925. Pendidikan tingginya (1925-30) ia peroleh pertama kali di Presidency College. Kemudian ketika hendak melanjutkan studinya ke Universitas Cambridge, ibunya jatuh sakit.

Subrahmanyan Chandrasekhar
Subrahmanyan Chandrasekhar
Born	(1910-10-19)October 19, 1910 Lahore, British India
Died	August 21, 1995(1995-08-21) (aged 84) Chicago, Illinois, United States
Residence	United States
Citizenship	India (1910–1953) United States (1953–1995)
Fields	Astrophysics
Institutions	University of Chicago University of Cambridge
Alma mater	Presidency College, Madras Trinity College, Cambridge
Doctoral advisor	R.H. Fowler, Arthur Stanley Eddington
Doctoral students	Donald Edward Osterbrock, Roland Winston, F. Paul Esposito, Jeremiah P. Ostriker
Known for	Chandrasekhar limit
Notable awards	Nobel Prize in Physics (1983) Copley Medal (1984) National Medal of Science (1966) Padma Vibhushan (1968)

Early life and education

 

 

 

Chandrasekhar was born on 19 October 1910 in Lahore, Punjab, India to a Tamil Iyer family Sitalakshmi (1891–1931) and Chandrasekhara Subrahmanya Iyer (1885–1960) who was posted in Lahore as Deputy Auditor General of the Northwestern Railways at the time of Chandrasekhar's birth. He was the eldest of their four sons and the third of their ten children. His paternal uncle was the Indian physicist and Nobel laureate C. V. Raman. C. S. Iyer. His mother was devoted to intellectual pursuits, had translated Henrik Ibsen's A Doll's House into Tamil and is credited with arousing Chandra's intellectual curiosity at an early age.

Chandrasekhar was tutored at home initially through middle school and later attended the Hindu High School, Triplicane, Madras during the years 1922-25. Subsequently, he studied at Presidency College, Madras from 1925 to 1930, writing his first paper, "The Compton Scattering and the New Statistics", in 1929 upon inspiration from a lecture by Arnold Sommerfeld and obtaining his bachelor's degree, B.Sc. (Hon.), in physics in June 1930.


In July 1930, Chandrasekhar was awarded a Government of India scholarship to pursue graduate studies at the University of Cambridge, where he was admitted to Trinity College, secured by Professor R. H. Fowler with whom he communicated his first paper. During his travels to England, Chandrasekhar spent his time working out the statistical mechanics of the degenerate electron gas in white dwarf stars, providing relativistic corrections to Fowler's previous work (see Legacy below).


In his first year at Cambridge, as a research student of Fowler, Chandrasekhar spent his time in intensive study, calculating mean opacities and applying his results to the construction of an improved model for the limiting mass of the degenerate star, and was introduced to the monthly meetings of the Royal Astronomical Society, where he met Professor E. A. Milne. At the invitation of Max Born he spent the summer of 1931, his second year of post-graduate studies, at Born’s institute at Göttingen, working on opacities, atomic absorption coefficients, and model stellar photospheres. On the advice of Prof. P. A. M. Dirac, he spent his final year of graduate studies at the Institute for Theoretical Physics in Copenhagen, where he met Prof. Niels Bohr.


After receiving a bronze medal for his work on degenerate stars, in the summer of 1933, Chandrasekhar was awarded his PhD degree at Cambridge with a thesis among his four papers on rotating self-gravitating polytropes, and the following October, he was elected to a Prize Fellowship at Trinity College for the period 1933-37. During this time, he made acquaintance with Sir Arthur Eddington. Chandrasekhar married Lalitha Doraiswamy in September 1936. He had met her as a fellow student, a year junior to him, at Presidency College, Madras. In his Nobel autobiography, Chandrasekhar wrote, "Lalitha's patient understanding, support, and encouragement have been the central facts of my life."




Chandrasekhar's infamous encounter with Arthur Eddington in 1935, in which the latter publicly ridiculed Chandra's most famous (and ultimately correct) discovery (see Chandrasekhar limit) led Chandra to consider employment outside of the U.K. (Later in life, Chandra on multiple occasions, expressed the view that Eddington's behavior was in part racially motivated.)


Masa Kuliah di Universitas Cambridge



Menurut tradisi India, ia harus tinggal di rumah merawat ibunya. Namun ibunya yang ingin anaknya sukses mendesak Chandra (nama kecil Chandrasekhar) untuk tetap pergi ke Cambridge, Inggris. 

Selama perjalanan panjang dengan kapal laut ke Inggris, Chandra mencoba menggabungkan pengetahuannya tentang bintang Bajang putih (white dwarf) dengan teori relativistik spesial, ia terkejut sekali mendapatkan hasil bahwa suatu bintang bajang putih dapat terbentuk melalui evolusi bintang, asalkan massa bintang itu kurang dari 1,45 massa matahari. 

Jika bintang terlalu berat maka gaya tolak akibat larangan Pauli tidak mampu menahan gaya gravitasi bintang, akibatnya bintang akan kolaps menjadi bintang netron atau bahkan menjadi lubang hitam (black hole). 

Tiba di Universitas Cambridge, dengan beasiswa penuh dari pemerintah India, Chandrasekhar menjadi mahasiswa peneliti di bawah bimbingan Profesor R.H. Fowler. Di tengah-tengah kesibukannya, Chandrasekhar masih ingat hasil perhitungannya di kapal laut itu. 

Ia mencoba menghitung ulang dan mendiskusikannya dengan para fisikawan di Cambridge, ternyata ia mendapatkan hasil yang sama bahwa ada batas atas massa bintang agar dapat berevolusi menjadi bintang bajang putih. 

Batas atas ini kemudian terkenal dengan nama “Chandrasekhar limit”. Karena hasil penelitian mengenai evolusi bintang inilah, 50 tahun kemudian Chandrasekhar dianugerahi hadiah nobel fisika (1983). 

Chandrasekhar sempat menghabiskan tahun ketiga masa kuliahnya di institut fisika teori, Copenhagen atas saran P.A.M. Dirac (pelopor fisika kuantum) yang melihat kemampuannya yang cemerlang. Pada tahun 1933, ia memperoleh gelar Ph.D dari Cambridge. 

Hanya beberapa bulan berselang, ia bergabung dengan Trinity College hingga tahun 1937. Ketika melakukan kunjungan ke Universitas Harvard, atas undangan Dr. Harlow Shapley selama musim dingin (Januari-Maret 1936), ia ditawari posisi sebagai peneliti di Universitas Chicago dan memutuskan menerima tawaran itu pada Januari 1937. 

Saat berada di Chicago, iapun melengkapi teorinya dan mempublikasikannya dalam buku An Introduction to the Study of Stellar Structure (1939). 

Riset bagi Chandrasekhar memang merupakan kerja berkesinambungan. 

Ia mencatat ada tujuh periode riset dalam hidupnya. 

Pertama, teori tentang struktur bintang, termasuk mengenai Bajang Putih (1929-39). 

Kedua, teori gerak Brownian yang merupakan bagian dari dinamika bintang (1938-43). 

Ketiga, teori tentang transfer energi, termasuk tentang atmosfer bintang dan teori kuantum ion negatif hidrogen, juga tentang atmosfer bintang (1943-50). 

Keempat, stabilitas hidrodinamika dan hidromagnetik (1953-61). 

Kelima, keseimbangan dan stabilitas bentuk elips, bagian dari kolaborasinya dengan Norman R Lebovitz (1961-8). Keenam, teori relativitas umum dan astrofisika relativitas (1962-71). 

Terakhir, teori matematika Black Holes (1974-83). Hasil penelitiannya itu dipublikasikan dalam berbagai monograf dan jurnal terkenal untuk astrofisika dan fisika.. 

Pimpinan Universitas Chicago, Hanna Gray pernah mengungkapkan kesannya terhadap Chandrasekhar. Profesor bidang astronomi dan astrofisika ini adalah ilmuwan yang penuh dedikasi, guru dari para guru, seseorang yang senantiasa membaktikan dirinya untuk kreativitas dunia ilmiah. 

Disamping fisika, Chandrasekhar juga menyukai bahasa Inggris dan senang membaca karya-karya sastra terkenal tulisan Shakespeare. 

Orang sangat mengagumi bahasa inggrisnya yang sangat sempurna baik dalam tata bahasa maupun aksennya, sampai-sampai fisikawan terkenal Hans Bethe mengatakan: 

"Chandrasekhar was one of the great astrophysicists of our time. He was also the greatest master of the English language that I know”. 

Sumber: Prof. Yohanes Surya, Ph.D.

Teleskop Luar Angkasa Hubble VIII

http://hubblesite.org/

Future

Equipment failure

A WFPC2 image of a small region of theTarantula Nebula in the Large Magellanic Cloud

Past servicing missions have exchanged old instruments for new ones, both avoiding failure and making possible new types of science. Without servicing missions, all of the instruments will eventually fail. In August 2004, the power system of the Space Telescope Imaging Spectrograph (STIS) failed, rendering the instrument inoperable. The electronics had originally been fully redundant, but the first set of electronics failed in May 2001.^[131] This power supply was fixed during servicing mission 4 in May 2009. Similarly, the main camera (the ACS) primary electronics failed in June 2006, and the power supply for the backup electronics failed on January 27, 2007.^[132] Only the instrument's Solar Blind Channel (SBC) was operable using the side-1 electronics. A new power supply for the wide angle channel was added during SM 4, but quick tests revealed this did not help the high resolution channel.^[133]As of late May 2009, tests of both repaired instruments are still ongoing.

HST uses gyroscopes to stabilize itself in orbit and point accurately and steadily at astronomical targets. Normally, three gyroscopes are required for operation; observations are still possible with two, but the area of sky that can be viewed would be somewhat restricted, and observations requiring very accurate pointing are more difficult.^[134] There are further contingency plans for science with just one gyro,^[135] but if all gyros fail, continued scientific observations will not be possible. In 2005, it was decided to switch to two-gyroscope mode for regular telescope operations as a means of extending the lifetime of the mission. The switch to this mode was made in August 2005, leaving Hubble with two gyroscopes in use, two on backup, and two inoperable.^[136] One more gyro failed in 2007.^[137] By the time of the final repair mission, during which all six gyros were replaced (with two new pairs and one refurbished pair), only three gyros were still working. Engineers are confident that they have identified the root causes of the gyro failures, and the new models should be much more reliable.^[138]

In addition to predicted gyroscope failure, Hubble eventually required a change of nickel hydrogen batteries. A robotic servicing mission including this would be tricky, as it requires many operations, and a failure in any might result in irreparable damage to Hubble. Alternatively, the observatory was designed so that during shuttle servicing missions it would receive power from a connection to the space shuttle, and this capability could have been utilized by adding an external power source (an additional battery) rather than changing the internal ones.^[139] In the end, however, the batteries were simply replaced during service mission 4.

Orbital decay

Hubble orbits the Earth in the extremely tenuous upper atmosphere, and over time its orbit decays due to drag. If it is not re-boosted by a shuttle or other means, it will re-enter the Earth's atmosphere sometime between 2019 and 2032, with the exact date depending on how active the Sun is and its impact on the upper atmosphere. The state of Hubble's gyros also affects the re-entry date, as a controllable telescope can be oriented to minimize atmospheric drag. Not all of the telescope would burn up on re-entry. Parts of the main mirror and its support structure would probably survive, leaving the potential for damage or even human fatalities (estimated at up to a 1 in 700 chance of human fatality for a completely uncontrolled re-entry).^[140] With the success of STS-125, the natural re-entry date range has been extended further as the mission replaced its gyroscopes, even though Hubble was not re-boosted to a higher orbit.

NASA's original plan for safely de-orbiting Hubble was to retrieve it using a space shuttle. The Hubble telescope would then have most likely been displayed in the Smithsonian Institution. This is no longer considered practical because of the costs of a shuttle flight, the mandate to retire the space shuttles years prior, and the risk to a shuttle's crew. Instead NASA looked at adding an external propulsion module to allow controlled re-entry.^[141] The final decision was not to attach a de-orbit module on STS-125, but to add a grapple fixture so a robotic mission could more easily attach such a module later.^[142]

Debate over final servicing mission

Main article: STS-125

Columbia was originally scheduled to visit Hubble again in February 2005. The tasks of this servicing mission would have included replacing a fine guidance sensor and two broken gyroscopes, placing protective "blankets" on top of torn insulation, replacing the Wide Field and Planetary Camera 2 with a new Wide Field Camera 3 and installing the Cosmic Origins Spectrograph (COS). However, then-NASA Administrator Sean O'Keefe decided that, in order to prevent a repeat of the Columbia accident, all future shuttles must be able to reach the 'safe-haven' of the International Space Station (ISS) should an in-flight problem develop that would preclude the shuttle from landing safely. The shuttle is incapable of reaching both the Hubble Space Telescope and the International Space Station during the same mission, and so future manned service missions were canceled.^[143]

This decision was assailed by numerous astronomers, who felt that Hubble was valuable enough to merit the human risk. HST's successor, the James Webb Space Telescope (JWST), will not be ready until well after the 2010 scheduled retirement of the space shuttle. While Hubble can image in the ultraviolet and visible wavelengths, JWST is limited to the infrared. The break in space-observing capabilities between the decommissioning of Hubble and the commissioning of a successor is of major concern to many astronomers, given the great scientific impact of HST taken as a whole.^[144] The consideration that the JWST will not be located in low Earth orbit, and therefore cannot be easily repaired in the event of an early failure, only makes these concerns more acute. Nor can JWST's instruments be easily upgraded. On the other hand, many astronomers felt strongly that the servicing of Hubble should not take place if the costs of the servicing come from the JWST budget.

In January 2004, O'Keefe said he would review his decision to cancel the final shuttle servicing mission to HST due to public outcry and requests from Congress for NASA to look for a way to save it. On 13 July 2004 an official panel from the National Academy of Sciencesmade the recommendation that the HST should be preserved despite the apparent risks. Their report urged "NASA should take no actions that would preclude a space shuttle servicing mission to the Hubble Space Telescope". In August 2004, O'Keefe requested the Goddard Space Flight Center to prepare a detailed proposal for a robotic service mission. These plans were later canceled, the robotic mission being described as "not feasible".^[145] In late 2004, several Congressional members, led by Sen. Barbara Mikulski (D-MD), held public hearings and carried on a fight with much public support (including thousands of letters from school children across the country) to get the Bush Administration and NASA to reconsider the decision to drop plans for a Hubble rescue mission.^[146]

The arrival in April 2005 of the new NASA Administrator, Michael D. Griffin, changed the status of the proposed shuttle rescue mission. At the time, Griffin stated he would reconsider the possibility of a manned servicing mission. Soon after his appointment, he authorized Goddard Space Flight Center to proceed with preparations for a manned Hubble maintenance flight, saying he would make the final decision on this flight after the next two shuttle missions. In October 2006 Griffin gave the final go-ahead for the mission. The 11-daySTS-125 mission by Atlantis was scheduled for launch in October 2008.^[147][148] However, the main data-handling unit failed in late September 2008, halting all reporting of scientific data. This unit has a backup, and on October 25, 2008 Hubble was successfully rebooted and was reported to be functioning normally.^[149] However, since a failure in the backup unit would now leave the HST helpless, the service mission was postponed to allow astronauts to repair this problem. This mission got underway on May 11, 2009^[150] and completed all the long planned replacements as well as additional repairs, including replacing the main data-handling unit.

Planned successors

Main articles: James Webb Space Telescope and Advanced Technology Large-Aperture Space Telescope

Several space telescopes are claimed to be successors to Hubble, and some ground based astronomy lays claim to higher optical achievements. None of the near-term space-based telescopes will duplicate Hubble's wavelength coverage (near ultra-violet to near infrared wavelength), instead concentrating on the farther infrared bands. These bands are preferred for studying high Z and low temperature objects, but cannot be studied from the ground, and cannot be retrofitted to the Hubble since it lacks the requisite cooled optics. None of the space-based successors are designed to be serviced on orbit. In contrast, ground based astronomy includes roughly the same wavelengths as Hubble, is catching up in terms of resolution (via adaptive optics), has much larger light gathering power, and is easily upgraded. However, it cannot yet match the Hubble's excellent resolution over a wide field of view, and the very dark background of space.

JWST plans to detect stars in the early Universe approximately 280 million years older than stars HST now detects.

The James Webb Space Telescope (JWST) is a planned infrared space observatory, and lays claim to being a planned successor of Hubble.^[151] The main scientific goal is to observe the most distant objects in the universe, beyond the reach of existing instruments. JWST will be able to detect stars in the early Universe approximately 280 million years older than stars HST now detects.^[152][153]

JWST is a NASA-led international collaboration between NASA, the European Space Agencyand the Canadian Space Agency. Formerly called the Next Generation Space Telescope (NGST), it was renamed after NASA's second administrator, James E. Webb, in 2002. The telescope's launch is planned for no earlier than June 2014. It will be launched on an Ariane 5rocket.^[154]

Another similar effort is the European Space Agency's Herschel Space Observatory, launched on May 14, 2009. Like JWST, Herschel has a mirror substantially larger than Hubble's, but observes only in the far-infrared.

Much further out is the Advanced Technology Large-Aperture Space Telescope (AT-LAST)^[155] is a proposed 8 to 16-meter (320 to 640-inch) optical space telescope that if approved, built, and launched (using the planned Space Launch System), would be a true replacement and successor for the Hubble Space Telescope (HST); with the ability to observe and photograph astronomical objects in the optical, ultraviolet, and Infrared wavelengths, but with substantially better resolution than Hubble.

Selected space telescopes & instruments[156]
Name	Year	Wavelength	Aperture
GALEX	2003	0.135-0.280 μm	0.5 m
Spitzer	2003	3-180 μm	0.85 m
Hubble STIS	1997	0.115-1.03 μm	2.4 m
Hubble WFC3	2009	0.2-1.7 μm	2.4 m
Herschel	2009	60-672 μm	3.5 m
JWST	Planned	0.6-10 μm	6.5 m

Existing ground based telescopes, and various proposed Extremely Large Telescopes, certainly exceed the HST in terms of sheer light gathering power, due to their much larger mirrors. In some cases, they may also be able to match or beat Hubble in resolution by using adaptive optics (AO). However, AO on large ground-based reflectors will not make Hubble and other space telescopes obsolete. Most AO systems sharpen the view over a very narrow field – Lucky Cam, for example, produces crisp images just 10" to 20" wide, whereas Hubble's cameras are super sharp across a 2½' (150") field. Furthermore, space telescopes can study the heavens across the entire electromagnetic spectrum, most of which is blocked by Earth's atmosphere. Finally, the background sky is darker in space than on the ground, because air absorbs solar energy during the day and then releases it at night, producing a faint—but nevertheless discernible—airglow that washes out faint, low-contrast astronomical objects.^[157]

See also

	Astronomy portal
	Spaceflight portal

• List of largest optical reflecting telescopes

References

• "Hubble Space Telescope Primer for Cycle 17" (PDF). STScI.
• Allen, Lew (1990). "The Hubble Space Telescope Optical Systems Failure Report" (PDF). NASA Technical Report NASA-TM-103443. The definitive report on the error in the Hubble mirror.
• Dunar, A. J.; S. P. Waring (1999). Power To Explore—History of Marshall Space Flight Center 1960–1990. U.S. Government Printing Office.ISBN 0-16-058992-4. Chapter 12, The Hubble Space TelescopePDF (260 KB). Covers the development of the telescope.
• Logsdon, John M.; Amy Paige Snyder, Roger D. Launius, Stephen J. Garber, and Regan Anne Newport (PDF). NASA SP-2001-4407: Exploring the Unknown — Selected Documents in the History of the U.S. Civil Space Program. Volume V: Exploring the Cosmos. NASA.. Contains many of the primary documents such as Spitzer's 1946 article, the Wood's Hole report on STScI autonomy, and the ESA memorandum of understanding. Also includes other NASA astronomy programs.
• Spitzer, Lyman S (1979). "History of the Space Telescope". Quarterly Journal of the Royal Astronomical Society 20: 29–36. Bibcode1979QJRAS..20...29S. PDF version here ^[158]PDF. Covers the early history of precursors and proposals.
• Tatarewicz, Joseph N. "Chapter 16: The Hubble Space Telescope Servicing Mission". NASA. From the book SP-4219: From Engineering Science To Big Science. A detailed account of the first servicing mission.
• Zimmerman, Robert F. The Universe in a Mirror — The Saga of the Hubble Space Telescope and the Visionaries Who Built It, publ. Princeton UP (2008, 2010)