Zitat von Livescience.com, 8 Jan. 2020The giant red star Betelgeuse might be harboring a gruesome secret in its past. A new model posits that the prominent night-sky object was once two stars, until the larger star ate its smaller companion. And that could explain several of Betelgeuse's peculiar properties. ... By closely monitoring Betelgeuse's surface, different researchers have calculated that the star's rotational rate is somewhere between 11,000 and 33,000 mph (17,700 to 53,000 km/h), Manos Chatzopoulos, an astronomer at Louisiana State University in Baton Rouge, said during a session on Monday (Jan. 6) at the 235th meeting of the American Astronomical Society here.
This is surprising because as a star ages and enters the red giant phase of its life, like Betelgeuse has, the star expands and its rotation typically slows down, much like an ice skater pushing out their arms to slow their spin, Chatzopoulos told Live Science.
Betelgeuse is also a runaway star, meaning that the object is zipping along at a mind-boggling speed, in Betelgeuse's case, 67,000 mph (108,000 km/h) relative to background stars in the Milky Way, he added.
"For such a famous star that everyone knows and loves, nobody has tried to explain the combination of these two things," Chatzopoulos said, referring to its odd rotation rate and speed. "So how do you put together these two facts?"
A clue might come from where Betelgeuse is thought to originate, a star-dense region known as the Orion OB1a association. Along with colleagues, Chatzopoulos has suggested that gravitational interactions with the many stars in that region could have flung Betelgeuse away at high speed millions of years ago, explaining the star's hyper-velocity.
Betelgeuse might have also had a smaller companion, the researchers posited, which got tossed out along with it. As Betelgeuse aged and expanded, it might have engulfed this partner, which would have stirred up Betelgeuse's outer layers "like stirring up coffee with a stick," Chatzopoulos said, and increased its rotation rate.
He and his collaborators have run sophisticated stellar-evolution computer models incorporating all these ideas. The results that best fit Betelgeuse’s observed features suggested it was once two separate stars, one with 16 times the sun's mass and another with four times the sun's mass. The researchers are preparing to submit their research to The Astrophysical Journal.
The researchers' models were also able to match the amount of nitrogen seen in Betelgeuse's atmosphere, which is unusually high. This is a potentially corroborating piece of evidence, because the stirring of a companion star might have dredged up nitrogen from Betelgeuse's center, Chatzopoulos said.
Earlier work by Chatzopoulos' former Ph.D. advisor offered the idea that Betelgeuse was formed as the merger of two stars. Chatzopoulos said that his new research expands on that prior idea and adds in specific simulations to account for the red giant star's rotation and speed.
Zitat It’s probably nothing: Gravitational wave burst detected near Betelgeuse Posted by Deborah Byrd in HUMAN WORLD | SPACE | January 15, 2020
Betelgeuse has dimmed recently, prompting some to wonder if it’s about to explode. An explosion might trigger a gravitational wave burst. Betelgeuse is still there. The nearby gravitational wave burst probably means nothing for this star. Still …
The Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo detectors recorded a “burst” of gravitational waves this week, from an area of sky near the red supergiant Betelgeuse. This unanticipated burst has been dubbed, for now, S200114f. It’s prompting some interesting chatter on Twitter because Betelgeuse has undergone an unusual dimming in recent weeks, and some astronomy enthusiasts have wondered if it were about to explode. Betelgeuse has not exploded. It’s still there. Still, a supernova explosion of Betelgeuse might be linked with a gravitational wave burst. As Jackson Ryan explained on CNET last night (January 14, 2020):
The gravitational waves we’ve detected so far usually relate to extreme cosmic events, like two black holes colliding or neutron stars finally merging after being caught in a death spiral. Burst gravitational waves have not been detected before and scientists hypothesize they may be linked to phenomena such as supernova or gamma ray bursts, producing a tiny ‘pop’ when detected by the observatories.
Zitat Andy Howell @d_a_howell MehrAndy Howell hat Dr. Jessie Christiansen retweetet Update on the Gravitational Wave burst from last night: - Betelgeuse is still there (as expected) - 400 sq. deg. is a large area - too big for most - You can see where telescopes have/are pointing here: http://treasuremap.space/alerts?graceids...ng_status=pandc … - ZTF has some faint candidates to investigate
Zitat Andy Howell @d_a_howell Also, from the lack of detection of neutrinos by KM3Net/ORCA, they calculate a lower limit on the distance for a core collapse origin of 6.1 kpc, or 20,000 lightyears. So not Betelgeuse! https://gcn.gsfc.nasa.gov/gcn3/26751.gcn3 15:50 - 14. Jan. 2020
Zitat Andy Howell Verifizierter Account @d_a_howell
Andy Howell hat Corey S. Powell retweetet
This depiction is right. When #Betelgeuse explodes it will be nearly as bright as the full moon and obvious all over the world. It will make astronomy an international conversation and inspire millions. Has anyone studied how wildlife will be affected? 11:59 - 17. Jan. 2020
Zitat Mauro Aguirre @MauroAguirreBr 17. Jan. Some one should make an ultra realistic CGI of what the Betelgeuse super nova will look like from earth. This will maybe satisfy a little this desire to see the real thing. Corey S. Powell @coreyspowell Antwort an @MauroAguirreBr This is the only realistic attempt I've seen so far to show what a #Betelgeuse supernova might look like. https://www.youtube.com/watch?v=_VjZdxgIMs4 …
Zu Supernovae als "Standardkerzen" für die Bestimmung kosmischer Entfernungen und, hier, die Hypothese der "dunklen Energie" als postuliertem Antrieb hinter der sich beschleunigenden Expansion des Weltalls. Wir haben eine neue Grundkontroverse in der Kosmologie.
"New evidence shows that the key assumption made in the discovery of dark energy is in error"
Zitat "The team has performed very high-quality (signal-to-noise ratio ~175) spectroscopic observations to cover most of the reported nearby early-type host galaxies of SN Ia, from which they obtained the most direct and reliable measurements of population ages for these host galaxies. They find a significant correlation between SN luminosity and stellar population age at a 99.5 percent confidence level. As such, this is the most direct and stringent test ever made for the luminosity evolution of SN Ia. Since SN progenitors in host galaxies are getting younger with redshift (look-back time), this result inevitably indicates a serious systematic bias with redshift in SN cosmology.
Other cosmological probes, such as the cosmic microwave background (CMB) and baryonic acoustic oscillations (BAO), are also known to provide some indirect and "circumstantial" evidence for dark energy, but it was recently suggested that CMB from Planck mission no longer supports the concordance cosmological model which may require new physics (Di Valentino, Melchiorri, & Silk 2019). Some investigators have also shown that BAO and other low-redshift cosmological probes can be consistent with a non-accelerating universe without dark energy (see, for example, Tutusaus et al. 2017). In this respect, the present result showing the luminosity evolution mimicking dark energy in SN cosmology is crucial and very timely.
This result is reminiscent of the famous Tinsley-Sandage debate in the 1970s on luminosity evolution in observational cosmology, which led to the termination of the Sandage project originally designed to determine the fate of the universe."
Zitat Nevertheless, to test the effect of luminosity evolution, in the discovery papers, Riess et al. (1998), Schmidt et al. (1998), and Perlmutter et al. (1999) only used morphological classification of host galaxies in the local universe as a proxy for stellar population age. Because of apparently very small difference in the standardized brightness between SNe Ia in the early-type and late-type host galaxies, they concluded that the luminosity evolution is negligible in SN cosmology. Later analysis based on a larger sample by Hicken et al. (2009), however, found a systematic difference of ∼0.14 mag between the very early- and very late-type galaxies (see also Suzuki et al. 2012). Recent investigations of host galaxies further found a correlation between the SN brightness1and host mass, suggesting that SNe Ia in less massive galaxies are ∼0.1 mag fainter than those in more massive galaxies (Kelly et al. 2010; Sullivan et al. 2010; Childress et al. 2013; Johansson et al. 2013). More recent studies based on star formation rate (SFR) in host galaxies also showed that the SNe Ia in locally star-forming environments are fainter than those in locally passive environments (Rigault et al. 2015; Kim et al. 2018; Rigault et al. 2018; Roman et al. 2018; Rose et al. 2019). (p.3)
Die Debatte zwischen den Positionen von Allen Sandage und Beatrice Tinsley ab 1972 drehte sich um den Wert der Hubble-Kosnante H; Sandage taxierte die nach der Entdeckung der ersten radiogalaxien 1967 auf einen Wert von 50 und kam damit auf ein Alter des Universums von 20 Milliarden Jahren; Tinsley vermutete, daß Galaxien im frühen Universum lichtschwächer gewesen seien und kan auf die Hälfte des Alters. Übrgiens nicht die erste Kontroverse dieser Art: die vorhergehende war die Entdeckung in den 1940er Jahren, daß es zwei Klassen von Cepheiden gab, wodurch sich die Entfernungen zu den dadurch bestimmten Galaxien auf einen Schlag verdopppelten.
"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire
"Betelgeuse is Continuing to Dim! It’s Down to 1.506 Magnitude"
Zitat von Universe Today.com 22 Jan 2020Villanova University astronomers Edward Guinan and Richard Wasatonic were the first to report Betelgeuse’s recent dimming. In a new post on The Astronomer’s Telegram, the pair of astronomers report a further dimming of Betelgeuse. They also point out that although the star is still dimming, its rate of dimming is slowing.
Betelgeuse is a red supergiant star in the constellation Orion. It left the main sequence about one million years ago and has been a red supergiant for about 40,000 years. It’s a core-collapse SN II progenitor, which means that eventually, Betelgeuse will burn enough of its hydrogen that its core will collapse, and it will explode as a supernova.
Zitat The Continued Unprecedented Fading of Betelgeuse ATel #13410; Edward F. Guinan and Richard J. Wasatonic (Villanova University) on 20 Jan 2020; 17:50 UT
We report further on the recent unusual dimming of the red supergiant Betelgeuse (alpha Ori) reported previously in ATel #13341 and ATel #13365. We continue to carry out V-band and Wing TiO and near-IR photometry of the star. Since our last report, Betelgeuse has continued to gradually decrease in brightness. Our most recent photometry secured on 17.25 UT and 18.20 UT January 2020 yields: V = +1.494 mag and 1.506 mag, respectively. This is more than ~0.2 mag fainter than previously reported in ATel #13365 on 22.25 UT Dec. 2019. However during the last week or so the decline in brightness of the star may be slowing. As reported by Brian Skiff of Lowell Observatory (priv. commun.) visual estimates of Betelgeuse are available as far back as about 180-years ago. Systematic visual measures of the star have been made by AAVSO observers since the 1920s. More precise photoelectric photometry began nearly 100 yrs ago but systematic (mostly unpublished) photometry of Betelgeuse commenced about 40-years ago at Villanova Observatory by Scott Wacker and Guinan. Betelgeuse is now nearly as faint as (the slightly variable) B2 star Bellatrix (V ~+1.62 mag). Bellatrix (gamma Ori) is about 5° west of Betelgeuse in the constellation Orion. The analysis of the calibrated Wing photometry (Wing 1992: JAAVSO 21, 42) returns measures of the temperature (via calibrated Wing TiO- and near-IR (B-C) color-indices) as well as estimates of bolometric magnitude (m-bol). The Wing intermediate band A-filter is used to measure the temperature-sensitive TiO 719-nm (gamma; 0, 0) molecular band. The B (750-nm) and C (1020.4-nm) filters are centered on relatively line-free stellar continuum regions. The C-band filter measures have been calibrated with K-M stars with bolometric magnitudes returning proxy measures of the apparent bolometric magnitude (m-bol) (see Wasatonic et al. 2015: PASP, 127, 1010). During the 25-years of V-band / Wing Near-IR photometry, Betelgeuse is currently the coolest and least luminous yet observed. Since September 2019, the star's temperature has decreased by ~100 K while its luminosity (inferred from the C-band/m-bol observations) has diminished by nearly 25%. At face value using R'/R = [(T'/T)^4 / L'/L]^0.5 (where R', T' and L' are the current values of stellar Radius, Temperature & Luminosity), this implies an increase of the star's radius of ~9%. However, as pointed out by others, the current fainting episode could also arise from expelled, cooling gas/dust partially obscuring the star. The recent changes defined by our V-band/Wing photometry seem best explained from changes in the envelop-outer convection atmosphere of this pulsating, unstable supergiant. If these recent light changes are due to an extra-large amplitude light pulse on the ~420-day period, then the next mid-light minimum is expected during late January/early February, 2020. If Betelgeuse continues to dim after that time then other possibilities will have to be considered.
"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire
Zitat von Sky and Telescope, 29 Jan 2020To see what Betelgeuse is up to anytime visit the AAVSO website. In the Pick a Star box, type Betelgeuse then either select Check Recent Observations or Plot a Light Curve. You can input your own parameters by selecting Plot Another Curve in the top left-hand corner. In the dialog boxes, you can include all observations in every color band or choose specific types such as visual, red, or V-band, for example. You can also toggle between Julian and calendar dates, and under Preferences you can set your magnitude scale.
ATel #13439; Edward F. Guinan and Richard J. Wasatonic (Villanova University) on 1 Feb 2020; 23:20 UT
We give an update on the star's recent behavior and also correct an error in our prior telegram (ATel #13410). Although the decrease in brightness appears to have slowed, our most recent observation on 30.15 UT, January 2020 is V = +1.614 +/-0.012 mag. The average of our last three measures over the prior 10-days is = +1.58 mag. Our V-mag measures are in very good agreement with corresponding values found by AAVSO observers. Betelgeuse is now ~1.0 mag fainter relative to observations made at the start of 2019/20 observing season during September. As discussed in the previous telegrams, Wing TiO and near-IR photometry returns measures of the star’s temperature (T) from TiO 719-nm band-head feature relative to the nearby reference continuum (the Wing B-filter at 752-nm). The Wing C-band filter (1024-nm) is centered on a (mostly) line-free spectral region near the peak of the M-star's spectral energy distribution (see Wing 1992: JAAVSO 21, 42). The Wing C-band observations serve as proxies for apparent bolometric magnitudes (m-bol) from which the star's luminosity(L) can be estimated. The analyses of the updated Wing ABC measures return estimates of Teff (T) and Luminosity (L). The recent mean values (T', L', R') were computed from observations made during the last 10-days of January 2020. These are compared with measures from September 2019 (L, T, R) made during the local light maximum. The star's radius (R) is estimated from L = 4 pi R^2 -sigma T^4. Correcting the error in our previous ATel (thanks to George Cooper for pointing this out), the change in radius R'/R is calculated from R'/R = [(L'/L)/(T'/T)^4 ]^0.25. Adopting T'/T = (3565 K /3650 K), and L'/L = 0.77, indicates an apparent radius decrease of R'/R ~0.92 since September 2019. But as a caveat, this estimate is bolometric-based and assumes the changes originate from a spherically symmetric star.
Zitat Betelgeuse Status @betelbot My visual mag from last night was 1.65 (robust mean of 11 observations). That is 0.06 mag dimmer than the robust mean of the 5 previous nights (n=87, 1.8σ). #Betelgeuse
3:03 nachm. · 8. Feb. 2020·betelbot
Ich vermeine das sogar mit unbewaffnetem Auge wahrnehmen zu können (bei klarem Himmel kann ich zurzeit Orion und Sirius von meinem Schreibtisch aus aufgehen sehen). Aber da mag die Erwartung die Wahrnehmung beeinflussen.
"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire
Zitat von Ulrich Elkmann im Beitrag #9Beteigeuze: täglicher Status auf Twitter.
Wie sich an den überaus witzigen Kommentaren ("blow up already!!") unschwer erkennen lässt, haben wir es hier mit einem Paradebeispiel dafür zu tun, dass ein Medium in seiner Dynamik halbwegs zu jener der Objekts passen sollte, über das berichtet wird.
Twitter eignet sich hervorragend, um bspw. über den aktuellen Stand eines Fussballspiels zu informieren. Über Ereignisse von kosmischer Dauer sollte man dann vielleicht doch eher ein Buch schreiben... oder eine Bibliothek. Die böte - im Gegensatz zu Twitter - darüberhinaus zumindest noch die theoretische Chance, dass die gesammelten Daten bei Eintritt des Sternentods in drölfzigtausend Jahren tatsächlich noch existieren. Besser noch wäre vermutlich eine Höhlenmalerei...
Zitat von F.Alfonzo im Beitrag #10Twitter eignet sich hervorragend, um bspw. über den aktuellen Stand eines Fussballspiels zu informieren.
Wir haben es hier ja genau mit dieser Dynamik zu tun: Momentaner Ist-Stand. Im Kosmos läuft es entweder in Jahrmillionen oder im Sekundentakt. Den Hintergrund habe ich (und die anderen zum Thema) ja anderweitig mitgeliefert. Die Natur des Sekundenmediums Twitter bringt es mit sich, daß man nur die jeweilige Meldung zu beachten hat und den Rattenschwanz der Reaktionen schlicht ignorieren muß. Wir sehen das ja exemplarisch bei @realDonaldTrump, wo i.d.R. in dem gefühlt erstem Tausend der auflaufenden Kommentare nur Geheule & Gepfeife vernehmbar ist. Wer Twitter-Kommentare zur Kenntnis nimmt, ist selbst schuld. Man bekommt die Kommis ja nur angezeigt, wenn man die Einzeltweets anklickt (was ich in diesem Fall gemacht hatte) & sich nicht den Gesamtstrang anschaut. Dort sieht man dann im Turnus den Stand der aktuellen Messungen, der Werte der letzen 120 Tage, und die mathematische Extrapolation der anstehenden Lichtkurve.
"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire
Zitat Betelgeuse Status @betelbot My visual mag from last night was 1.58 (robust mean of 19 observations). That is 0.02 mag brighter than the robust mean of the 5 previous nights (n=79, 0.4σ).
3:04 nachm. · 12. Feb. 2020
"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire
Zitat Betelgeuse Status @betelbot My visual mag from last night was 1.55 (robust mean of 17 observations). That is 0.04 mag brighter than the robust mean of the 5 previous nights (n=93, 1.0σ).
Zitat SPHERE public outreach @SPHERE_outreach SPHERE resolves the changing surface of the red giant Betelgeuse while it is dimming. At the same time thermal Infrared images obtained with VISIR support the hypothesis that large amount of dust is responsible for the dimming. Results by @Astro_MiguelM @PierreKervella
Zitat von The Astronomers' Telegram # 13512, 22 Feb 2020Three recent observations made at Wasatonic Observatory, carried out on 18.15 UT, 20.1 and 22.07 UT February 2020, returned V = +1.585 mag , +1.574 mag, and +1.522 mag, respectively. Photometry carried out by D. Carona on 18.2 UT February 2020 returned V = +1.589 mag. In addition, Wing TiO band and near-IR measures (and corresponding temperatures and luminosities) also reached minimum values during mid-February 2020. Photometry carried out by D. Carona (Texas A&M Univ.) on 18.2 UT February 2020 returned V = +1.589 mag. Also T. Calderwood's recent observations given on the AAVSO website (https://www.aavso.org/lcg) are: V = +1.589 mag, +1.567 mag and 1.556 mag, respectively on ~17.2, 19.2, 20.2 UT February 2020. Based on these and additional observations, Betelgeuse has definitely stopped dimming and has started to slowly brighten. Thus this "fainting" episode is over but additional photometry is needed to define the brightening phase. An ESO VLT/SPHERE IR image of Betelgeuse was secured during late 2019 December by M. Montarges et al. (2020: paper in preparation). The stunning VLT/SPHERE image shows that most of lower half of star has significantly dimmed, thus providing a spatially resolved image of the star informing about the observed dimming. (https://www.eso.org/public/news/eso2003/). At the time of the VLT/SPHERE observations, Betelgeuse's brightness was V ~ +1.3 mag.
Die Helligkeitskurve der Beteigeuze ist nun offensichtlich in ein exponentielles Wachstum übergegangen. Die Gefahren von zuviel Licht (Overillumination) dürfen nicht länger bagatellisiert werden. Menschen können davon sterben. Die Regierung verschläft das Problem. Alle Fenster müssen jetzt innerhalb weniger Wochen mit lichtdichten Vorhängen ausgestattet werden, notfalls zumauern. Wir müssen uns darauf einstellen, in Zukunft nur noch mit Sofi-Brillen nach draußen zu gehen. Am besten bleiben wir zuhause. Sonnenöl mit Lichtschutzfaktor 1000 wird es erst in einigen Jahren geben, trotz intensiver Forschung. Ratschläge aus dem Internet, sich einstweilen mit Schweröl zu behelfen, sind unverantwortlich. Panikmache ist allerdings nicht angebracht. Die Beteigeuze-Krise hat auch Vorteile, besonders für die Umwelt, da Straßenlampen nicht mehr gebraucht werden. Anleger sollten jetzt Aktien von Photovoltaik-Herstellern kaufen.
Zitat Betelgeuse: Nearby 'supernova' star's dimming explained By Paul Rincon Science editor, BBC News website 29 June 2020
Various scenarios have been put forward to explain the recent changes in the brightness of the star.
Astronomers have previously considered that dust produced by the star was obscuring it, causing the steep decline in brightness.
Red giants exhibit a behaviour known as pulsation, caused by changes in the area and temperature of the star's surface layers. Pulsations can eject the outer layers of the star with relative ease.
According to the study, which was led by Thavisha Dharmawardena from the Max Planck Institute for Astronomy in Heidelberg, Germany, the result isn't compatible with the presence of dust.
Instead, the astronomers say, temperature variations in the photosphere - the luminous surface of the star - most likely caused the brightness to drop.
"Corresponding high-resolution images of Betelgeuse from December 2019 show areas of varying brightness. Together with our result, this is a clear indication of huge star spots covering between 50% and 70% of the visible surface and having a lower temperature than the brighter photosphere," said co-author Peter Scicluna from the European Southern Observatory (Eso).
"For comparison, a typical sunspot is the size of the Earth. The Betelgeuse star spot would be a hundred times larger than the Sun. The sudden fading of Betelgeuse does not mean it is going supernova. It is a supergiant star growing a super-sized star spot." said co-author Prof Albert Zijlstra from The University of Manchester, UK.
3. Juli, 4:45. Ganz nebenbei: Venus als strahlender Morgenstern im Osten, zwanzig Grad über dem taubenblau schieferfarbenen Horizont. Zwischen tiefblauen Cumulonimbusbänken. Es gibt sie noch, die kleinen ästhetischen Satisfaktionen.
"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire
7. Juli. Robert A. Heinleins 113. Geburtstag. 4:19. Am Osthimmel Venus als strahlender Morgenstern, 20 Grad über dem Horizont. -3. Größenklasse, ein silberner Punkt ins taubenblaue Himmelsgewölbe gestanzt.
"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire
Doch als die irischen Forscher vom Trinity College in Dublin mit dem Very Large Telescope (VLT) der Europäischen Südsternwarte (Eso) nach einem „guten alten Bekannten“ in dieser Galaxie im Sternbild Wassermann erneut Ausschau hielten, war dieser Stern verschwunden. Einfach weg. Die Forscher sprechen von einem kosmischen Mysterium.
„Wir waren sehr überrascht, dass der Stern nicht mehr da war“, sagt Andrew Allan, Hauptautor der jetzt in den „Monthly Notices of the Royal Astronomical Society“ erschienenen Fachveröffentlichung.
Zitat von Florian im Beitrag #21Der Fall vom verschwundenen Stern.
Pressenotiz:
Zitat Using the X-SHOOTER and the ESPRESSO (Echelle Spectrograph for Rocky Exoplanet- and Stable Spectroscopic Observation) instruments on ESO’s Very Large Telescope (VLT), astronomers have monitored a massive luminous blue variable star in a compact dwarf galaxy called PHL 293B and surprisingly observed the sudden disappearance of the stellar signatures. They think this could indicate that the star either became less bright and partially obscured by dust or collapsed into a black hole without producing a supernova.
Also known as the Kinman Dwarf, PHL 293B lies approximately 75 million light-years away in the constellation of Aquarius.
In the 2000-2010s, astronomers studied a mysterious giant star in this galaxy and their observations indicated the star, which is some 2.5 million times brighter than the Sun, was in a late stage of its evolution.
Trinity College Dublin astronomer Andrew Allan and colleagues wanted to find out more about how very massive stars end their lives, and the object in PHL 293B seemed like the perfect target.
But when they pointed VLT to the galaxy in 2019, they could no longer find the telltale signatures of the star.
“Instead, we were surprised to find out that the star had disappeared,” Dr. Allan said.
Luminous blue variables are unstable, showing occasional dramatic shifts in their spectra and brightness.
Zitat The possible disappearance of a massive star in the low-metallicity galaxy PHL 293B Andrew P Allan, Jose H Groh, Andrea Mehner, Nathan Smith, Ioana Boian, Eoin J Farrell, Jennifer E Andrews Monthly Notices of the Royal Astronomical Society, Volume 496, Issue 2, August 2020, Pages 1902–1908
In der SF-/E.T.-mäßigen Spekulationsabteilung, Zeitmarke 1960er, war das "Verschwinden von Sternen" ein Anzeichen für die Entstehung einer Kardaschow/Kardazhev-Zivilisation vom Typ II, die eine Dyson-Sphäre um ihr Heimatgestirn errichtet hat, um sämtliche Strahlung als Energiequelle nutzen zu können. Freeman Dyson hat das in seinem grundlegenden Aufsatz (in Science, 1960) als mögliches Erkennungszeichen dafür vorgeschlagen. (Als weiteres Erkennungszeichen hat er vorgeschlagen, zu untersuchen, ob die Strahlung nicht doch weiter, aber in den Infrarotbereich verschoben, emittiert wird; bei völliger Absorption der Energie heizt sich die Innenseite einer solchen Sphäre im Lauf der Zeit auf die ambiente Oberflächentemperatur des umschlossenen Sterns auf.
Zitat At that distance, making out individual stars is impossible - we simply don't have the technology.
However, there's a type of star called a luminous blue variable that has a recognisable light signature. These stars are massive - on the supergiant or hypergiant scale - and at the end of their lives. As such, they are extremely bright and unstable, and their light can vary dramatically in both brightness and spectrum as they undergo outbursts and eruptions.
In the earlier observations of the dwarf galaxy, this signature was present, indicating a star between 2.5 and 3.5 million times as bright as the Sun. ... In recent years, however, evidence has started to emerge that stars can indeed collapse directly into black holes without undergoing a supernova explosion. In 2017, a paper was published on a similar phenomenon in a galaxy 22 million light-years away - a red giant star that brightened suddenly before blinking out of existence, leading astronomers to hypothesise that the star had undergone a failed supernova before collapsing.
It's not impossible that the star underwent an undetected supernova, but such a massive star as a luminous blue variable would be expected to produce a supernova afterglow that shines in the sky for at least five years following the kaboom.
"We may have detected one of the most massive stars of the local Universe going gently into the night," said astrophysicist Jose Groh of Trinity College Dublin.
It's impossible to know for certain with the current data. Only future observations across a range of wavelengths can shed light on the mystery of the missing star.
Hat ihn. Wie vermutet: bei diesem "Stern" könnte es sich möglicherweise um ein Daten-Artefakt handeln. Bzw. deren unzutreffende Interpretation.
Zitat Early studies of emission line galaxies have shown that objects that spectroscopically resembled H II regions both in line emission intensities and widths, constituted about 80 per cent of total samples,the rest being galaxies of Seyfert type (see e.g. French 1980,and references therein). Some of these objects are also characterized by their compacticity and blue excess as shown on photographic plates and represent the overlap between blue compact galaxies (BCG) and H II galaxies. PHL 293B is one of these objects. It was found by Haro & Luyten (1962) in the ‘Palomar–Haro–Luyten’ survey of faint blue objects. Kinman (1965) obtained its optical spectrum and described it as having a faint continuum with unresolved emission in the Balmer series and [O III] λλ 5007, 4959 and 4363 Å that makes of it, to our knowledge, one of the first detections of the [O III] λ 4363 Å auroral line in a star-forming galaxy. ... PHL 293B also looks compact in the images obtained by Cairos et al. (2001), and Geha et al. (2006) give an effective radius for this galaxy of only 0.4 kpc. Its absolute magnitude according to the Sloan Digital Sky Survey (SDSS) is Mg=−14.77. These facts make of it a very low luminosity and compact HII galaxy.
One of the characteristics of HII galaxies is their high star formation rate that takes place in a very small volume and probably in short duration episodes, thus making these galaxies easily observable. Given the large value of the equivalent width (EW) of their emission lines, it is the current burst of star formation that dominates their luminosity at blue and visible wavelengths. The low metallicity of these objects guarantees that they are in a chemically unevolved stage probably similar to what is expected in galaxies of early cosmological times. ... PHL 293B, also known as HL 293B, Kinman’s dwarf, A2228-00 and SDSS J223036.79-000636.9, is a very low luminosity galaxy(MB=−14.37; Cairos et al.2001) at a distance of 23.1 Mpc obtained from the radial velocity (Mould et al.2000) taken from NASA/IPAC Extragalactic Database (NED) corrected for Virgo Infall, Great Attractor and Shapley, with a Hubble constant of 73 km s−1 Mpc −1.Its metallicity was first measured by French (1980) who gave a valueof 12+log(O/H) = 7.78 and, more recently, by Izotov et al. (2007) who derive a value of 12+log(O/H)=7.66 from SDSS data.
Der entscheidende Passus ist dieser:
Zitat 5.3 The absorption lines of Fe II multiplet 42
An important clue for an alternative interpretation of the absorptions seen at λ4939 and λ5031 Å is given by the discovery of a previously unidentified absorption at λ∼5183 Å (Fig.3) corresponding to λ5155 Å in the rest frame of the forbidden lines and λ5169 Å in the rest frame of the blueshifted Balmer absorptions. This absorption is real and is present in the spectra from SDSS, VLT-UVES, VLT-X-shooter and WHT-ISIS that were taken in four different epochs (see Fig.10). Although the λ∼5183 Å absorption could be attributed to Mg2 λ5172 Å present in late star spectra, this possibility can be readily dismissed given that the observed wavelength would imply a shift of 1050 km s−1 with respect to the galaxy rest frame and definitely inconsistent with the presence of the CaT lines at the galaxy velocity rest frame.
A more plausible interpretation is that we are in fact detecting the Fe II multiplet (42) λλ 4923.93, 5018.44 and 5169.03 Å blueshifted by the same amount as the Balmer absorption features i.e. ∼800 km s−1 to λλ4911, 5005 and 5155 Å. These absorptions have already been detected in a variety of transient luminous objects like the LBV candidate NGC 2366-V1 or SNe IIn like 1995G, 1999el or 1999eb among others (see fig. 2 of Di Carlo et al.2002).
LBVs represent a short (∼10^4 yr) phase in the evolution of massive stars during which the star undergoes luminous outbursts associated with large mass-loss events. During these short phases lasting few years the LBV can reach, in extreme cases, 10^6 L or Mv∼−10 and luminosity variations of ∼1 mag. The luminosity changes are in general correlated with spectral changes. The typical absolute magnitude of an LBV in quiescent state is Mv∼−6. In general, information about LBVs is very sparse given that only 35 candidates have been identified in our galaxy (Clark, Larionov & Arkharov2005). Only two of these, η Car and P Cygni, were observed during an outburst. Extragalactic examples are known due to either photometric or specific spectral variability. The mechanism responsible for the outbursts remains unidentified.
"High-velocity blueshifted Fe II absorption in the dwarf star-forming galaxy PHL 293B: evidence for a wind driven supershell?" Roberto Terlevich, Elena Terlevich, Guillermo Bosch, Angeles Díaz, Guillermo Hagele, Monica Cardaci and Veronica Firpo, MNRAS 45, 1449-1461 (2014)
Wenn meine Vermutung zutrifft (das ist jetzt aus der Hüfte geschossen), dann hätten wir es mit einem Fall zu tun wie bei Harry Houdinis Verschwindenlassen des Elefanten im New Yorker Hippodrom am 7. Januar 1918. (Der Elefant befand sich nie auf der Bühne.) In der Astronomie ist das durchaus Tagesgeschäft - man denke etwa an das LGM-Signal von 1967 oder den "Marsleben!"-Meteoriten ALH0084.
"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire
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