Example of a supernova
Epoch J2000 Equinox
|Right ascension||09h 20m 34.30s|
|Declination||+50° 41′ 46.80″|
|Apparent magnitude (V)||17.716 (R)|
|Distance||156,200,000 pc (509,000,000 ly) pc|
iPTF14hls is an unusual supernova star that has erupted continuously for about 1,000 days before becoming a remnant nebula. It had previously erupted in 1954. None of the theories nor proposed hypotheses fully explain all aspects of the object.
The star iPTF14hls was discovered in September 2014 by the Intermediate Palomar Transient Factory, and it was first made public in November 2014 by the CRTS survey as CSS141118:092034+504148. Based on that information it was confirmed as an exploding star in January 2015. It was thought then that it was a single supernova event (Type II-P) that would dim in about 100 days, but instead, it continued its eruption for about 1,000 days while fluctuating in brightness at least five times. The brightness varied by as much as 50%, going through five peaks. Also, rather than cooling down with time as expected of a Type II-P supernova, the object maintains a near-constant temperature of about 5000–6000 K. Checks of photographs from the past found one from 1954 showing an explosion in the same location. Since 1954, the star has exploded six times.
The principal investigator is Iair Arcavi. His international team used the Low Resolution Imaging Spectrometer (LRIS) on the Keck I telescope to obtain the spectrum of the star's host galaxy, and the Deep Imaging and Multi-Object Spectrograph (DEIMOS) on Keck II to obtain high-resolution spectra of the unusual supernova itself.
The host galaxy of iPTF14hls is a star-forming dwarf galaxy, implying low metal content, and the weak iron-line absorption seen in the supernova spectra are consistent with a low metallicity progenitor. The study estimates that the star that exploded was at least 50 times more massive than the Sun. The researchers also remark that the debris expansion rate is slower than any other known supernova by a factor of 6, as if exploding in slow-motion. However, if this were due to relativistic time dilation then the spectrum would be red-shifted by the same factor of 6, which is inconsistent with their observations. In 2017 the expansion speed was constrained to approximately 1,000 km/s.
Arcavi's team continue monitoring the object in other bands of the spectrum in collaboration with additional international telescopes and observatories. These facilities include the Nordic Optical Telescope and NASA's Swift space telescope, the Fermi Gamma-ray Space Telescope, while the Hubble Space Telescope began to image the location in December 2017.
iPTF14hls is an ongoing event, and after about 1,000 days, its light displayed a dramatic drop, but the supernova is still visible, and by November 2018 its spectra had become a remnant nebula. A high-resolution image of this latest phase was obtained with the Hubble Space Telescope.
Current theory predicts that the star would consume all its hydrogen in the first supernova explosion, and depending on the initial size of the star, the remnants of the core should form a neutron star or a black hole, so it is thought that there is a novel unidentified phenomenon happening. There is no known theory that explains the observation. None of the hypotheses listed below can explain the continued presence of hydrogen or the energetics observed. According to Iair Arcavi, this discovery requires refinement of existing explosion scenarios, or the development of a new scenario, that can:
- produce the same spectral signatures as common Type IIP supernovae but with an evolution slowed down by a factor of 6 to 10.
- provide energy to prolong the light curve by a factor of ~6 while not introducing narrow-line spectral features or strong radio and X-ray emission indicative of circumstellar material interaction.
- produce at least five peaks in the light curve.
- decouple the deduced line-forming photosphere from the continuum photosphere.
- maintain a photospheric phase with a constant line velocity gradient for over 600 days.
One hypothesis involves burning antimatter in a stellar core; this hypothesis holds that massive stars become so hot in their cores that energy is converted into matter and antimatter, causing the star to become extremely unstable, and undergo repeated bright eruptions over periods of years. Antimatter in contact with matter would cause an explosion that blows off the outer layers of the star and leaves the core intact; this process can repeat over decades before the large final explosion and collapse to a black hole.
Pulsational pair-instability supernova
Another hypothesis is the pulsational pair-instability supernova, a massive star that may lose about half its mass before a series of violent pulses begins. On every pulse, material rushing away from the star can catch up with earlier ejected material, producing bright flashes of light as it collides, simulating an additional explosion (see Supernova impostor). However, the energy released by the iPTF14hls supernova is more than the theory predicts.
Another hypothesis, based on the light spectrum, suggests it is a clear signature of shock interaction of ejected material with dense circumstellar material.
In December 2017, a team using the Fermi Gamma-ray Space Telescope reported that they may have detected in iPTF14hls, for the first time, high energy gamma-ray emission from a supernova. The gamma-ray source appears ∼ 300 days after the explosion of iPTF14hls, and is still observable, but more observations are needed to verify that iPTF14hls is the exact source of the observed gamma-ray emission. If the association between the gamma-ray source and iPTF14hls is real, there are difficulties to model its gamma-ray emission in the framework of particle acceleration in supernova ejecta produced shock. The energy conversion efficiency needs to be very high, so it is suggested that a jet (anisotropic emission) from a close companion may be necessary to explain some of the observed data. No X-ray emissions have been detected, which makes the interpretation of the gamma-ray emission a difficult task.
Common envelope jets
This hypothesis suggests common envelope jets supernova (CEJSN) impostors resulting from a neutron star companion. It proposes "a new type of repeating transient outburst initiated by a neutron star entering the envelope of an evolved massive star, accreting envelope material and subsequently launching jets which interact with their surroundings." The ejecta could reach velocities of 10000 km/s despite not being a supernova.
- Eta Carinae, a massive star undergoing similar eruptions
- Arcavi, Iair; et al. (2017). "Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star" (PDF). Nature. 551 (7679): 210. arXiv:1711.02671. Bibcode:2017Natur.551..210A. doi:10.1038/nature24030. PMID 29120417.
- Late-time observations of the extraordinary Type II supernova iPTF14hls. (PDF) arXiv — Astronomy & Astrophysics. J. Sollerman, F. Taddia, I. Arcavi, C. Fremling1, C. Fransson, J. Burke, S. B. Cenko, O. Andersen, I. Andreoni, C. Barbarino, N. Blagorodova, T. G. Brink, A. V. Filippenko, A. Gal-Yam1, D. Hiramatsu, G. Hosseinzadeh, D. A. Howell, T. de Jaeger, R. Lunnan, C. McCully, D. A. Perley, L. Tartaglia1, G. Terreran, S. Valenti, X. Wang. Submitted on November 8, 2018.
- 'Zombie' star survived going supernova. By Paul Rincon, BBC News. 8 November 2017.
- This star cheated death, exploding again and again. Lisa Grossman, Science News. 8 November 2017.
- "The CRTS Survey". crts.caltech.edu. Retrieved 2017-11-15.
- "Detection of CSS141118:092034+504148".
- Li, Wenxiong; Wang, Xiaofeng; Zhang, Tianmeng (2015-01-01). "Spectroscopic Classification of CSS141118:092034+504148 as a Type II-P Supernova". The Astronomer's Telegram. 6898. Bibcode:2015ATel.6898....1L.
- Joel Hruska (10 November 2017). "Astronomers Find Star That Has Exploded Six Times". Retrieved 26 November 2017.
- Astronomers Discover A Star That Would Not Die. W. M. Keck Observatory. 8 November 2017.
- Astronomers discover a star that would not die. Astronomy Now. 9 November 2017.
- Peculiar Supernovae. Dan Milisavljevic1, and Raffaella Margutti. arXive. 9 May 2018.
- Andrews JE, Smith N (2017). Strong late-time circumstellar interaction in the notso-impossible supernova iPTF14hls. ArXiv e-prints 1712.00514
- Bizarre 3-Year-Long Supernova Defies Our Understanding of How Stars Die. Harrison Tasoff, Space. 8 November 2017.
- Fermi Large Area Telescope detection of gamma-ray emission from the direction of supernova iPTF14hls (PDF). Noam Soker1, Avishai Gilkis. arXiv, Preprint 20 December 2017.
- What Type of Star Made the One-of-a-kind Supernova iPTF14hls?. Arcavi, Iair. HST Proposal id.15222. Cycle 25. August 2017.
- Scientists on new supernova: WTF have we been looking at?. John Timmer, Ars Technica. 8 November 2017.
- 'Zombie star' amazes astronomers by surviving multiple supernovae. Ian Sample, The Guardian. 8 November 2017.
- Models for the Unusual Supernova iPTF14hls. Stan E. Woosley. arXive, 26 January 2018.
- This Star Went Supernova … And Then Went Supernova Again. Jake Parks, Discovery Magazine. 9 November 2017.
- A magnetar model for the hydrogen-rich super-luminous supernova iPTF14hls. Luc Dessart, Astronomy & Astrophysics. Volume 610, 22 February 2018. doi:10.1051/0004-6361/201732402
- Strong late-time circumstellar interaction in the peculiar supernova iPTF14hls. Jennifer E Andrews, Nathan Smith. Monthly Notices of the Royal Astronomical Society, Volume 477, Issue 1, 11 June 2018, Pages 74–79. doi:10.1093/mnras/sty584
- Fermi Large Area Telescope detection of gamma-ray emission from the direction of supernova iPTF14hls. Qiang Yuan, Neng-Hui Liao, Yu-Liang Xin, Ye Li, Yi-Zhong Fan, Bing Zhang, Hong-Bo Hu, Xiao-Jun Bi. ArXiv. 1 February 2018.
- Common envelope jets supernova (CEJSN) impostors resulting from a neutron star companion. Avishai Gilkis, Noam Soker, Amit Kashi. arXive. 1 March 2018.
- Explaining iPTF14hls as a common envelope jets supernova. Noam Soker1, Avishai Gilkis. arXiv. Preprint 20 December 2017.
- A fallback accretion model for the unusual Type II-P supernova iPTF14hls. (PDF) arXiv — Astronomy & Astrophysics. L. J. Wang, X. F. Wang, S. Q. Wang, Z. G. Dai, L. D. Liu, L. M. Song, L. M. Rui, Z. Cano, B. Li. Sumbitted to arXiv on October 2, 2018.
- Light curves and spectra on the Open Supernova Catalog
- This star refuses to die, even after it explodes - engadget
- The star that blew up a little... Then blew up a lot - SyFyWire