Hanny's Voorwerp

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Hanny's Voorwerp
Hannys voorwerp.jpg
Object type Quasar ionization echo
Other designations SDSS J094103.80+344334.2
Observation data
(Epoch J2000)
Constellation Leo Minor
09h 41m 03.81s
Declination +34° 43′ 34.3″
Distance 6.5×108 ly

In visual light (V)

Notable features
Associated with spiral galaxy IC 2497
SDSS J094103.80+344334.2
Commons page Related media on Wikimedia Commons

Hanny's Voorwerp /ˈhʌn.nis ˈvɔːr.wɛrp/, (Dutch for Hanny's object) is a rare type of astronomical object called a quasar ionization echo.[1][2] It was discovered in 2007 by Dutch schoolteacher Hanny van Arkel, while she was participating as a volunteer in the Galaxy Zoo project. Photographically, it appears as a bright blob close to spiral galaxy IC 2497 in the constellation Leo Minor.


Hanny's Voorwerp (HsV) is about the size of a small galaxy and has a central hole over 16,000 light years across. In an image taken with the HST, HsV is colored green, a standard false color that is used to represent the presence of several luminous emission lines of glowing oxygen. HsV has been shown to be at the same distance from Earth as the adjacent galaxy IC 2497, which is about 650 million light-years away.

Star birth is occurring in the region of HsV that faces IC 2497. Radio observations indicate that this is due to an outflow of gas arising from the IC 2497's core which is interacting with a small region of HsV to collapse and form stars. The youngest stars are several million years old.[3]


HST zooms in on a space oddity

One hypothesis suggests that HsV consists of remnants of a small galaxy showing the impact of radiation from a bright quasar event that occurred in the center of IC 2497 about 100,000 years before how it is observed today.[4] The quasar event is thought to have stimulated the bright emission that characterizes HsV. The quasar might have switched off in the last 200,000 years and is not visible in the available images.[3] This might well be due to a process known as AGN feedback.[5]

One possible explanation for the missing light-source is that illumination from the assumed quasar was a transient phenomenon. In this case, its effects on HsV would be still visible because of the distance of several tens of thousands of light years between HsV and the quasar in the nearby galaxy: HsV would show a "light echo" or "ghost image" of events that are older than those currently seen in the galaxy.[6]

On 17 June 2010, a group of researchers at the European VLBI Network (EVN) and the UK’s Multi-Element Radio Linked Interferometer Network (MERLIN), proposed another related explanation. They hypothesized that the light comes from two sources: (1) a supermassive black hole at the center of IC 2497, and (2) light produced by an interaction of an energetic jet from the black hole and the gas surrounding IC 2497.[7]


NGC 7252. This picture was taken by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory.

In February 2012, authors W. C. Keel and others published a paper in the Monthly Notices of the Royal Astronomical Society titled "The Galaxy Zoo survey for giant AGN-ionized clouds: past and present black hole accretion events".[8] As a result of the interest in similar ionized clouds for the study of both the history and obscuration of Active Galactic Nucleus (AGN), participants in the Galaxy Zoo (GZ) project carried out a wide search for such clouds using data from the Sloan Digital Sky Survey (SDSS). This search yielded a list of 19 galaxies with AGN-photoionized clouds detected to beyond 10 kiloparsecs from the nuclei.[8] These were nicknamed 'Voorwerpjes' from the Dutch for 'small objects'.

In August 2013, F. Schweizer and others published a paper in the Astrophysical Journal titled "The [O III] Nebula of the Merger Remnant NGC 7252: A Likely Faint Ionization Echo".[9] This reports the finding of a Voorwerpje on the outskirts of the well-studied NGC 7252.

In August 2014, W.C. Keel and others published a pre-print on arXiv of a paper submitted to the Astrophysical Journal named:" HST Imaging of Fading AGN Candidates I: Host-Galaxy Properties and Origin of the Extended Gas".[10] This studies 8 of the original 19 Voorwerpjes in greater detail, focusing on 'the host-galaxy properties and origin of the gas.' Among the telescopes used was the 6 meter BTA-6 at the Special Astrophysical Observatory of the Russian Academy of Science.

One example of voorwerpjes are the galaxies UGC 12914 and 12915, which are merging, and in the process of merging, the smaller UGC 12915 formed a small voorwerpje near it.



Michael Nielsen (2011) - Reinventing Discovery: The New Era of Networked Science. Princeton University Press. ISBN 978-0-691-14890-8.

Chris Lintott, Brian May, Patrick Moore (2012) - The Cosmic Tourist: The 100 Most Awe-inspiring Destinations in the Universe. Carlton Publishing Group. ISBN 978-1847326195

Patrick Moore, Chris North (2012) - The Sky at Night: Answers to Questions from Across the Universe. BBC Books. ISBN 978-1849903462

Stephen P. Maran (2012 3rd edit.) - Astronomy For Dummies. John Wiley & Sons. ISBN 978-1118376973

Nitin Agarwal, Merlyna Lim, Rolf T. Wigand (2014) - Online Collective Action: Dynamics of the Crowd in Social Media (Lecture Notes in Social Networks). Springer. ISBN 978-3709113394

Marc J. Kuchner (2011) - Marketing for Scientists: How to Shine in Tough Times. Island Press. ISBN 978-1597269940

Michael A. Seeds, Dana E. Backman (2011) - Foundations of Astronomy. Brooks/Cole Cengage Learning. ISBN 9780538733533


  1. ^ Rincon, P. (5 August 2008). "Teacher finds new cosmic object". BBC News. Retrieved 19 October 2012. 
  2. ^ Keel, W. C.; et al. (2012). "The History and Environment of a Faded Quasar: Hubble Space Telescope Observations of Hanny's Voorwerp and IC 2497". The Astrophysical Journal 144 (2): 66. arXiv:1206.3797. Bibcode:2012AJ....144...66K. doi:10.1088/0004-6256/144/2/66. 
  3. ^ a b "Hubble Zooms in on a Space Oddity". European Southern Observatory. Retrieved 11 January 2011. 
  4. ^ "Stars in their eyes: An armchair astronomer discovers something very odd". The Economist. 26 June 2008. Retrieved 30 June 2008. 
  5. ^ Fabian, A. C. (2012). "Observational Evidence of Active Galactic Nuclei Feedback". Annual Review of Astronomy and Astrophysics 50: 455. arXiv:1204.4114. Bibcode:2012ARA&A..50..455F. doi:10.1146/annurev-astro-081811-125521. 
  6. ^ "'Cosmic ghost' discovered by volunteer astronomer". Phys.org. 5 August 2008. 
  7. ^ Baldwin, E. (25 June 2010). "Radio observations shed new light on Hanny's Voorwerp". Astronomy Now. 
  8. ^ a b Keel, W. C.; et al. (2012). "The Galaxy Zoo survey for giant AGN-ionized clouds: past and present black hole accretion events". Monthly Notices of the Royal Astronomical Society 420 (1): 878. arXiv:1110.6921. Bibcode:2012MNRAS.420..878K. doi:10.1111/j.1365-2966.2011.20101.x. 
  9. ^ Schweizer, F.; Seitzer, P.; Kelson, D.; Villanueva, E.; Walth, G. (2013). "The [O III] Nebula of the Merger Remnant NGC 7252: A Likely Faint Ionization Echo". The Astrophysical Journal 773 (2): 148. arXiv:1307.2233. Bibcode:2013ApJ...773..148S. doi:10.1088/0004-637X/773/2/148. 
  10. ^ W.C. Keel, W.P.Maksym, V.N. Bennert, C.J. Lintott, S.D.Chojnowski, A. Moiseev, A. Smirnova, K. Schawinski, C.M. Urry, D.A. Evans, A. Pancoast, B. Scott, C. Showley, K. Flatland (2014). "HST Imaging of Fading AGN Candidates I: Host-Galaxy Properties and Origin of the Extended Gas". arXiv:1408.5159v1. Bibcode:2014arXiv1408.5159K. 

External links[edit]