IPTF14hls

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iPTF14hls
IPTF14hls.png
Supernova iPTF14hls before and after detection
Observation data
Epoch J2000 [1]        Equinox
Constellation Ursa Major
Right ascension 09h 20m 34.30s [1]
Declination +50° 41 46.80 [1]
Apparent magnitude  (V)17.716 (R) [1]
Astrometry
Distance 156,200,000  pc (509,000,000  ly) [1]   pc
Database references
SIMBAD data

iPTF14hls is an unusual supernova star that erupted continuously for about 1,000 days beginning in September 2014 [2] before becoming a remnant nebula. [3] It had previously erupted in 1954. [4] None of the theories nor proposed hypotheses fully explain all the aspects of the object.

Contents

Observations

The star iPTF14hls was discovered in September 2014 by the Intermediate Palomar Transient Factory, [5] and it was first made public in November 2014 by the CRTS survey [6] as CSS141118:092034+504148. [7] Based on that information it was confirmed as an exploding star in January 2015. [8] [4] 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 [3] while fluctuating in brightness at least five times. [1] The brightness varied by as much as 50%, [4] going through five peaks. [5] 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. [1] Checks of photographs from the past found one from 1954 showing an explosion in the same location. [4] Since 1954, the star has exploded six times. [9]

The principal investigator [10] 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. [11]

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. [1] The study estimates that the star that exploded was at least 50 times more massive than the Sun. [12] 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. [1] In 2017 the expansion speed was constrained to approximately 1,000  km/s . [13] [14]

Ongoing observations

Arcavi's team continue monitoring the object in other bands of the spectrum in collaboration with additional international telescopes and observatories. [15] These facilities include the Nordic Optical Telescope and NASA's Swift space telescope, the Fermi Gamma-ray Space Telescope, [16] while the Hubble Space Telescope began to image the location in December 2017. [15] [17]

iPTF14hls was an ongoing event into 2018, when after about 1,000 days, its light displayed a dramatic drop, but the event remained visible, [3] and by November 2018 its spectra had become a remnant nebula. [3] A high-resolution image of this latest phase was obtained with the Hubble Space Telescope during Cycle 25 (October 1, 2017 to September 30, 2018). [3]

Hypotheses

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. [1] [5] [4] However, these mechanisms are unable to reproduce the observed light curve with its very long bright plateau and multiple brighter peaks. [17] [18] None of the hypotheses published before early 2018 — the first three listed below — could explain the continued presence of hydrogen or the energetics observed. [19] [20] According to Iair Arcavi, this discovery requires refinement of existing explosion scenarios, or the development of a new scenario, that can: [1]

  1. produce the same spectral signatures as common Type IIP supernovae but with an evolution slowed by a factor of 6 to 10.
  2. 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.
  3. produce at least five peaks in the light curve.
  4. decouple the deduced line-forming photosphere from the continuum photosphere.
  5. maintain a photospheric phase with a constant line velocity gradient for over 600 days.

Antimatter

One hypothesis involves burning antimatter in a stellar core; [5] 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. [21] 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. [12]

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. [1] [19] 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. [12]

Magnetar

Magnetar models can also explain many of the observed features, but give a smooth light curve and may require an evolving magnetic field strength. [20] [22]

Shock interaction

Jennifer E Andrews and Nathan Smith hypothesised that the observed light spectrum is a clear signature of shock interaction of ejected material with dense circumstellar material (CSM). They proposed that a typical explosion energy, with "enveloped" or "swallowed" CSM interaction — as seen in some recent supernovae, including SN 1998S, SN 2009ip, and SN 1993J — could "explain the peculiar evolution of iPTF14hls." [23]

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. [16] 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. [16] 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. [16] No X-ray emissions have been detected, which makes the interpretation of the gamma-ray emission a difficult task. [24]

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." [25] [26] The ejecta could reach velocities of 10,000 km/s despite not being a supernova. [25]

Fall-back accretion

One team suggests the possibility that the observed slow expansion may be an effect of fall-back accretion, and presented a model. [3] [27]

Variable hyper-wind

A long-term outflow similar to stellar winds with variable mass-loss rates rather than a sudden outburst like supernovae could fit the data of the light curve not only of iPTF14hls, but also of Eta Carinae. The observations could be a result of extreme wind from very massive stars. [28]

See also

Related Research Articles

<span class="mw-page-title-main">Supernova</span> Explosion of a star at its end of life

A supernova is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star or when a white dwarf is triggered into runaway nuclear fusion. The original object, called the progenitor, either collapses to a neutron star or black hole, or is completely destroyed to form a diffuse nebula. The peak optical luminosity of a supernova can be comparable to that of an entire galaxy before fading over several weeks or months.

<span class="mw-page-title-main">SN 1987A</span> 1987 supernova event in the constellation Dorado

SN 1987A was a type II supernova in the Large Magellanic Cloud, a dwarf satellite galaxy of the Milky Way. It occurred approximately 51.4 kiloparsecs from Earth and was the closest observed supernova since Kepler's Supernova. 1987A's light reached Earth on February 23, 1987, and as the earliest supernova discovered that year, was labeled "1987A". Its brightness peaked in May, with an apparent magnitude of about 3.

<span class="mw-page-title-main">Gamma-ray burst</span> Flashes of gamma rays from distant galaxies

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<span class="mw-page-title-main">Superluminous supernova</span> Supernova at least ten times more luminous than a standard supernova

A super-luminous supernova is a type of stellar explosion with a luminosity 10 or more times higher than that of standard supernovae. Like supernovae, SLSNe seem to be produced by several mechanisms, which is readily revealed by their light-curves and spectra. There are multiple models for what conditions may produce an SLSN, including core collapse in particularly massive stars, millisecond magnetars, interaction with circumstellar material, or pair-instability supernovae.

<span class="mw-page-title-main">Messier 108</span> Galaxy in the constellation Ursa Major

Messier 108 is a barred spiral galaxy about 28 million light-years away from Earth in the northern constellation Ursa Major. It was discovered by Pierre Méchain in 1781 or 1782. From the Earth, this galaxy is seen almost edge-on.

<span class="mw-page-title-main">Type Ia supernova</span> Type of supernova in binary systems

A Type Ia supernova is a type of supernova that occurs in binary systems in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf.

<span class="mw-page-title-main">SN 1994D</span> Type Ia supernova

SN 1994D was a Type Ia supernova event in the outskirts of galaxy NGC 4526. It was offset by 9.0″ west and 7.8″ south of the galaxy center and positioned near a prominent dust lane. It was caused by the explosion of a white dwarf star composed of carbon and oxygen. This event was discovered on March 7, 1994 by R. R. Treffers and associates using the automated 30-inch telescope at Leuschner Observatory. It reached peak visual brightness two weeks later on March 22. Modelling of the light curve indicates the explosion would have been visible around March 3-4. A possible detection of helium in the spectrum was made by W. P. S. Meikle and associates in 1996. A mass of 0.014 to 0.03 M in helium would be needed to produce this feature.

<span class="mw-page-title-main">Type Ib and Ic supernovae</span> Types of supernovae caused by a star collapsing

Type Ib and Type Ic supernovae are categories of supernovae that are caused by the stellar core collapse of massive stars. These stars have shed or been stripped of their outer envelope of hydrogen, and, when compared to the spectrum of Type Ia supernovae, they lack the absorption line of silicon. Compared to Type Ib, Type Ic supernovae are hypothesized to have lost more of their initial envelope, including most of their helium. The two types are usually referred to as stripped core-collapse supernovae.

<span class="mw-page-title-main">Type II supernova</span> Explosion of a star 8 to 45 times the mass of the Sun

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<span class="mw-page-title-main">Pair-instability supernova</span> Type of high-energy supernova in very large stars

A pair-instability supernova is a type of supernova predicted to occur when pair production, the production of free electrons and positrons in the collision between atomic nuclei and energetic gamma rays, temporarily reduces the internal radiation pressure supporting a supermassive star's core against gravitational collapse. This pressure drop leads to a partial collapse, which in turn causes greatly accelerated burning in a runaway thermonuclear explosion, resulting in the star being blown completely apart without leaving a stellar remnant behind.

<span class="mw-page-title-main">Gamma-ray burst progenitors</span> Types of celestial objects that can emit gamma-ray bursts

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<span class="mw-page-title-main">NGC 7424</span> Galaxy in the constellation Grus

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<span class="mw-page-title-main">NGC 5806</span> Spiral galaxy in the constellation Virgo

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References

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