The Hubble Space Telescope: 21 Years and Counting
Total Page：16
File Type：pdf, Size：1020Kb
Mem. S.A.It. Vol. 83, 393 c SAIt 2012 Memorie della The Hubble Space Telescope: 21 years and counting N. Panagia1;2;3 1 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA 2 Istituto Nazionale di Astrofisica – Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123 Catania, Italy 3 Supernova Ltd, OYV #131, Northsound Road, Virgin Gorda, British Virgin Islands e-mail: [email protected] Abstract. I summarize the current status of the Hubble Space Telescope (HST) and illus- trate some of its exciting results. Key words. Telescopes: HST – Cosmology: observations – Dark Matter – Early Universe – Galaxies: Magellanic Clouds – Stellar Populations – Stars: V838 Mon – Planetary System – Comet: SL9 – Planets and Satellites: Pluto 1. Introduction After SM3B, HST’s science instruments in- cluded a spectrograph, the Space Telescope After twenty one years in orbit, the now “adult” Imaging Spectrograph (STIS) operating in the Hubble Space Telescope (HST) continues to UV and optical domains, and three cam- play a major role in astronomical research, and eras, the Wide Field - Planetary Camera 2 is undoubtedly one of the most important and (WFPC2), the Advanced Camera for Surveys most prolific space astronomy missions of all (ACS), the Near Infrared Camera - Multiobject time. Spectrograph (NICMOS), which was revived HST was deployed in low-Earth orbit in mission 3B with the installation of a (about 600 km) by the crew of the space mechanical cooling system, and the Fine shuttle Discovery (STS-31) on 25 April 1990. Guidance Sensors (FGS, primarily used for as- Although at the beginning the mission looked trometric observations). severely faulted because of spherical aberra- However, STIS stopped operations in tion, the first maintenance mission (STS-61 August 2004, leaving HST without a proper Endeavour, December 1993) fully restored the spectrographic capability, and ACS failed in functionality of HST. In fact, all HST servic- January 2007, leaving in operation rather old ing missions so far, namely SM1 in December instruments. Subsequently, HST suffered a se- 1993, SM2 in February 1997, SM3A in rious malfunction on September 27, 2008, with December 1999, and SM3B in February- a failure of the Science Instrument/Control March 2002 were enormous successes. & Data Handling system, which prevented data from the science instruments being trans- Send offprint requests to: N. Panagia mitted to the ground. On October 15, 2008, 394 Panagia: HST at 21 HST switched to operations on the redun- Among the HST high impact science we dant side of the data transmission system, and can mention the definitive measurement of the later resumed science observations with Wide- expansion rate of the Universe, the so-called Field Planetary Camera 2 (WFPC2) and the Hubble constant, the confirmation and charac- Advanced Camera for Surveys Solar Blind terization of massive black holes in the centers channel (ACS/SBC). of galaxies, the detection of the host galaxies Triumphally, in mid-Spring 2009 HST was of QSOs, and the exhaustive study of the prop- reborn with the Servicing Mission 4 (SM4). erties of the intergalactic medium that tell us Originally, SM4 was planned for 2004, about the chemical evolution of the Universe. but was postponed after the Columbia Space Even more exciting are the discoveries Shuttle tragedy in 2003 and then canceled in that were totally unanticipated and that have light of Agency safety concerns. Following opened new avenues to our knowledge of the the successful recovery of the Shuttle program cosmos, such as the discovery of the accelera- and a re-examination of SM4 risks, NASA ap- tion of the Universe, which may imply the ex- proved one last servicing mission. The rein- istence of the so-called “dark energy” that has stated SM4 was initially scheduled for flight in been dominating the expansion of the Universe Fall 2008, but, after the failure of a side of the in the last 8 billion years (e.g., Panagia 2005a), data transmission system, it was postponed to the properties of extremely distant galaxies as late Spring 2009. shown by the Hubble Deep Fields, as well On May 11, 2009, SM4 (STS125) started the Hubble Ultra-Deep Field observations that with the shuttle Atlantis taking seven astro- have provided us the direct view at thousands nauts to reach the HST, do all repairs and new of galaxies formed just a few hundred million installations on the telescope in five very in- years after the Big Bang, clues to the nature tense EVA (ExtraVehicular Activity) sessions, of gamma-ray burst sources that are possibly and come back safely on May 24, 2009. the most energetic explosions in the Universe, The two new cutting-edge instruments that the formation of planets in disks around young enhance Hubble’s capabilities by large fac- stars, the full characterization of planets orbit- tors, are the Cosmic Origins Spectrograph ing around other stars but our own Sun, and the (COS) and the Wide Field Camera 3 (WFC3). dramatic collision of comet Shoemaker-Levy 9 Astronauts also succeeded in the first ever on- fragments with Jupiter’s atmosphere. orbit repair of two existing instruments - both With so many exciting results, one should STIS and ACS. A refurbished Fine Guidance write a thick book to do justice to all of them Sensor has replaced one degrading unit of three and to the other many important discoveries now onboard, and will maintain a robust ability that HST has enabled us to make. Here, I shall to point the telescope. In addition, new gyros, highlight some of the recent discoveries made batteries and thermal blankets were installed to possible by Hubble. Summaries of previous ensure Hubble functions efficiently for a min- years most exciting HST results may be found imum of five, and possibly ten years after ser- in Panagia (1999, 2005b, 2010). vicing. 3. Cosmology and the distant Universe 2. HST results 3.1. The evolution of galaxies and the In 21 years HST has made more than 1,000,000 cosmic star formation rates observations, obtaining almost 500,000 images of about 30,000 different fields. The Hubble Deep Field observations, made Observations made with the HST have ei- with the WFPC2 in selected pointings of ther solved problems that had been under de- the Northern and the Southern hemispheres bate for many years, or have revealed quite un- (Williams et al. 1996, 2000) opened the way expected and exciting new phenomena. to the study of really high redshift galaxies, Panagia: HST at 21 395 tion up to z∼ 6:5 and characterizing not only the colors but also the morphologies of faint sources. The primary instrument was ACS, but WFPC2, NICMOS and STIS were also used in parallel. The HUDF consists of a single ultra-deep field (412 orbits in total) within the Chandra Deep Field South (Giacconi et al. 2002) in the GOODS area (Giavalisco et al. 2004). The adopted pointing was selected so as to avoid the gaps with the lowest effective exposure Fig. 1. The Hubble Ultra Deep Field as imaged with on the Chandra ACIS image of CDFS. The the HST-ACS. Also shown are the position, and the HUDF field was also selected to be accessible corresponding NICMOSand Spitzer-IRAC NIR im- to most major observatories in both Northern ages (inserts), of the massive galaxy HUDF-JD2, and Southern hemispheres. which is estimated to be at a redshift z ∼ 6:5, the The ACS exposure time was divided most distant galaxy identified in the HUDF. [Credit: B. Mobasher, NASA, ESA] among four filters, F435W (B435), F606W (V606), F775W (i775), and F850LP (z850), to give approximately uniform limiting mag- namely as high as z ∼ 5 and just about 1.5 bil- nitudes mAB ∼ 29 for point sources. The lion years after the Big Bang. HST observations were carried out between The original Northern hemisphere HDF re- late September 2003 and mid-January 2004. vealed a population of small, irregular galaxies The HUDF field contains at least 10,000 that often appeared in pairs or small groups. objects, the vast majority of which are galaxies. Much of the light from these objects was of Three samples of galaxies in different redshift high surface brightness, owing to high rates of intervals were identified in the HUDF from ob- star formation, but concentrated, requiring the jects with missing flux in the shortest wave- resolution of HST to identify them as distant length bands, those that ”dropped out” of the galaxies as opposed to red stars, for example. B435, V606, or i775 filters, corresponding ap- The extension of the deep-field approach to the proximately to three redshift ranges, namely southern hemisphere (Williams et al. 2000) 3.5-4.7, 4.6-5.5, and 5.7-7, respectively. The confirmed the main conclusions of the HDF main findings can be summarized as (Beckwith but also showed the limitations of a small field et al. 2006): survey in drawing broad conclusions about dis- • Galaxies at these high redshifts are smaller tant populations, i.e. cosmic error within small and less symmetric in shape than galaxies fields can be substantial. at lower redshifts. These results confirm that With the installation of a more efficient galaxies evolved rapidly in the first few billion camera, the ACS, deeper and deeper studies years after the Big Bang. were pursued, reaching with the Hubble Ultra • The faint sources detected by the HUDF are Deep Field (HUDF) survey objects at redshifts smaller on average than the brighter objects as high as ∼ 7 (Beckwith et al. 2006, Mobasher seen in shallower surveys such as GOODS et al. 2005). (Giavalisco et al. 2004) or the HDFs (Williams The Hubble Ultra Deep Field (HUDF) was et al.