Date of the discovery: 1 October 2009

Short Description: Hanny’s Voorwerp is the first Voorwerp discovered. It was first discovered by Hanny van Arkel in the galaxy zoo website. It is located near the galaxy IC 2497 as a fuzzy green cloud. The green colour comes from doubly ionized oxygen [O III], but the spectra revealed also ionized Helium [He II] and Neon [Ne V]. Star-formation cannot be accounted for this highly ionized gas. The current model describes an active galaxy nucleus (AGN) or quasar that released enough energy in the form of a particle jet, which then ionized a cloud of material. The cloud keeps emitting photons even after the AGN switched off. Later similar objects were discovered and were called Voorwerpjes (Keel et al. 2012). Voorwerp means “object” in Dutch and Voorwerpje means “small object”.

Volunteer(s): Hanny van Arkel

Researchers in the discovery paper: Chris J. Lintott, Kevin Schawinski, William Keel, Hanny Van Arkel, Nicola Bennert, Edward Edmondson, Daniel Thomas, Daniel J. B. Smith, Peter D. Herbert, Matt J. Jarvis, Shanil Virani, Dan Andreescu, Steven P. Bamford, Kate Land, Phil Murray, Robert C. Nichol, M. Jordan Raddick, Anže Slosar, Alex Szalay, Jan Vandenberg

Link to paper in ADS: https://ui.adsabs.harvard.edu/abs/2009MNRAS.399..129L/abstract

SIMBAD page: http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=IC+2497&submit=SIMBAD+search

Telescopes involved: Apache Point Observatory (SDSS 2.5m telescope), Isaac Newton Telescope (INT), Kitt Peak National Observatory (KPNO) 2.1-m telescope, 0.9-m telescope of the Southeastern Association for Research in Astronomy (SARA), 4.2-m William Herschel Telescope (WHT), UV/Optical Telescope (UVOT) and the X-Ray Telescope (XRT)

Figure 6 of the paper, WHT spectrum showing the strong [O III] lines, as well as the [He II] and [Ne V] lines that revealed the nature of the Voorwerps
Other pages:

wikipedia: https://en.wikipedia.org/wiki/Hanny’s_Voorwerp

Press Release: https://blog.galaxyzoo.org/2009/06/29/voorwerps-everywhere/

Personal website of Hanny van Arkel: https://www.hannysvoorwerp.com/3-voorwerp-in-the-pictures/

Project website: galaxy zoo

Credit for the header image: NASA, ESA, William Keel (Univ. Alabama)

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