The History of the Discovery of Sgr A*
At the center of the Milky Way hides a four-million solar mass black hole. The confirmation of its existence, which took place thanks to the study of star orbits conditioned by its immense gravity, earned the Nobel Prize 2020 for physics to Andrea Ghez and Reinhard Genzel. But the story of the observations that led to the discovery of this supermassive black hole begins in the 1950s and deserves to be told
A Luminous Quasar at Redshift 7.642
Distant quasars are unique tracers to study the formation of the earliest
supermassive black holes (SMBHs) and the history of cosmic reionization.
Despite extensive efforts, only two quasars have been found at z≥7.5, due
to a combination of their low spatial density and the high contamination rate
in quasar selection. We report the discovery of a luminous quasar at z=7.642,
J0313−1806, the most distant quasar yet known. This quasar has a bolometric
luminosity of 3.6×1013L⊙. Deep spectroscopic observations
reveal a SMBH with a mass of (1.6±0.4)×109M⊙ in this quasar.
The existence of such a massive SMBH just ∼670 million years after the Big
Bang challenges significantly theoretical models of SMBH growth. In addition,
the quasar spectrum exhibits strong broad absorption line (BAL) features in CIV
and SiIV, with a maximum velocity close to 20% of the speed of light. The
relativistic BAL features, combined with a strongly blueshifted CIV emission
line, indicate that there is a strong active galactic nucleus (AGN) driven
outflow in this system. ALMA observations detect the dust continuum and [CII]
emission from the quasar host galaxy, yielding an accurate redshift of 7.6423±0.0013 and suggesting that the quasar is hosted by an intensely
star-forming galaxy, with a star formation rate of ∼200 M⊙ yr−1 and a dust mass of ∼7×107 M⊙. Followup observations
of this reionization-era BAL quasar will provide a powerful probe of the
effects of AGN feedback on the growth of the earliest massive galaxies.
FLUCTUATIONS IN THE ELECTRO-FORCE FROM THE DAWN OF TIME… tell the tale of a maelstrom, the oldest and mightiest of the ur-gyres:
The Earliest Supermassive Black Hole and Quasar in the Universe
The most distant quasar known has been discovered. The quasar, observed
just 670 million years after the Big Bang, is 1000 times more luminous
than the Milky Way. It is powered by the earliest known supermassive
black hole, which weighs in at more than 1.6 billion times the mass of
the Sun. Seen more than 13 billion years ago, this fully formed distant
quasar is also the earliest yet discovered, providing astronomers with
insight into the formation of massive galaxies in the early Universe.
A Search for Technosignatures around 31 Sun-like Stars with the Green Bank Telescopeat 1.15–1.73GHz
We conducted a search for technosignatures in April of 2018 and 2019 with the L-band receiver (1.15-1.73 GHz) of the 100 m diameter Green Bank Telescope. These observations focused on regions surrounding 31 Sun-like stars near the plane of the Galaxy. We present the results of our search for narrowband signals in this data set as well as improvements to our data processing pipeline. Specifically, we applied an improved candidate signal detection procedure that relies on the topographic prominence of the signal power, which nearly doubles the signal detection count of some previously analyzed data sets. We also improved the direction-of-origin filters that remove most radio frequency interference (RFI) to ensure that they uniquely link signals observed in separate scans. We performed a preliminary signal injection and recovery analysis to test the performance of our pipeline. We found that our pipeline recovers 93% of the injected signals over the usable frequency range of the receiver and 98% if we exclude regions with dense RFI. In this analysis, 99.73% of the recovered signals were correctly classified as technosignature candidates. Our improved data processing pipeline classified over 99.84% of the ~26 million signals detected in our data as RFI. Of the remaining candidates, 4539 were detected outside of known RFI frequency regions. The remaining candidates were visually inspected and verified to be of anthropogenic nature. Our search compares favorably to other recent searches in terms of end-to-end sensitivity, frequency drift rate coverage, and signal detection count per unit bandwidth per unit integration time.
Our Galaxy, the Milky Way, possesses a supermassive black hole at its
centre, but its brightness is surprisingly low, typically 10–8
that of an active galactic nucleus (AGN) with similar black hole mass.
However, recent observations suggest that a huge amount of energy is
stored in the halo as X-ray emitting gas at a temperature T ≈ 2 × 106 K (ref. 1). Moreover, the presence of a Galactic wind blowing from the nucleus has been observed in radio, ultraviolet and X-rays2,3,4.
This wind may be the result of past episodes of activity. Astronomers
are now adding one more decisive piece to confirm the turbulent history
of our Galaxy. Writing in Nature, Peter Predehl and collaborators5 present the deepest X-ray all-sky map ever achieved with eROSITA6.
They have confirmed that a pair of symmetrical X-ray bubbles emerge
from the Galactic Centre, extending over 80–85° (14 kpc) above and below
the Galactic Plane. These bubbles were probably formed by strong shocks
during an explosion that happened over 15 million years ago, when the
Milky Way centre was 100 million times brighter than it is presently.
The total energy of the shock-heated X-ray emitting gas amounts to ~1056
erg, sufficient to perturb the structure, energy content and chemical
enrichment of the circum-Galactic medium of the Milky Way.
What Does the Closest Brown Dwarf Look Like?
…we identify four properties that are shared between the visual
lightcurve of this object and the infrared lightcurves of other objects:
1) The lightcurves remain variable over long periods (years); 2) The
lightcurve shape evolves, yet it displays characteristic period, which
is likely the rotational period of the object (as found in Apai et al.
2017); 3) In spite of the rapid evolution of the lightcurve, the
amplitudes over rotational time-scales remain similar and characteristic
to the object; 4) The lightcurves tend to be symmetric in the sense of
similar amount of positive–negative features, in contrast to, for
example, a situation in which a single positive feature appears
periodically on an otherwise flat lightcurve, which would indicate a
single bright spot in the atmosphere.
[…]
“No telescope is large enough to provide detailed images of planets or brown dwarfs. But by measuring how the brightness of these rotating objects changes over time, it is possible to create crude maps of their atmospheres – a technique that, in the future, could also be used to map Earthlike planets in other solar systems that might otherwise be hard to see… Our study provides a template for future studies of similar objects on how to explore – and even map – the atmospheres of brown dwarfs and giant extrasolar planets without the need for telescopes powerful enough to resolve them visually.”
wuh oh, that’s not a supernova, it’s (maybe) a star being eaten by a black hole! -
ASASSN-14ko is a Periodic Nuclear Transient in ESO 253-G003
We present the discovery that ASASSN-14ko is a periodically flaring AGN at
the center of the galaxy ESO 253-G003. At the time of its discovery by the
All-Sky Automated Survey for Supernovae (ASAS-SN), it was classified as a
supernova close to the nucleus. The subsequent six years of V- and g-band
ASAS-SN observations reveal that ASASSN-14ko has nuclear flares occurring at
regular intervals. The seventeen observed outbursts show evidence of a
decreasing period over time, with a mean period of P0=114.2±0.4 days
and a period derivative of P˙=−0.0017±0.0003. The most recent
outburst in May 2020, which took place as predicted, exhibited spectroscopic
changes during the rise and a had a UV bright, blackbody spectral energy
distribution similar to tidal disruption events (TDEs). The X-ray flux
decreased by a factor of 4 at the beginning of the outburst and then returned
to its quiescent flux after ~8 days. TESS observed an outburst during Sectors
4-6, revealing a rise time of 5.60±0.05 days in the optical and a decline
that is best fit with an exponential model. We discuss several possible
scenarios to explain ASASSN-14ko’s periodic outbursts, but currently favor a
repeated partial TDE. The next outbursts should peak in the optical on UT
2020-09-7.4±1.1 and UT 2020-12-26.5±1.4.
Investigating Transit - Part 1
The story starts in the 1960s with a fleet of satellites called NAVSAT, a satellite constellation for military navigation. While satellites were only launched between 1956 and 1988, one satellite in the constellation has refused to die and entered “zombie” status, enter Transit-5B5.
Transit-5B5 (launched in 1964) is the oldest “working” satellite, broadcasting an intermittent signal when not eclipsed in the 137MHz band. Interestingly enough, its actual navigation systems failed with in 19 days of launch, and it only continues to broadcast telemetry. Below is an image of Transit-5B5’s downlink as seen in SDR# (image from happysat.nl), this post will attempt to do basic analysis of one of the downlinks.
TIC 168789840: A Sextuply-Eclipsing Sextuple Star System
We report the discovery of a sextuply-eclipsing sextuple star system from TESS data, TIC 168789840, also known as TYC 7037-89-1, the first known sextuple system consisting of three eclipsing binaries. The target was observed in Sectors 4 and 5 during Cycle 1, with lightcurves extracted from TESS Full Frame Image data. It was also previously observed by the WASP survey and ASAS-SN. The system consists of three gravitationally-bound eclipsing binaries in a hierarchical structure of an inner quadruple system with an outer binary subsystem. Follow-up observations from several different observatories were conducted as a means of determining additional parameters. The system was resolved by speckle interferometry with a 0.“42 separation between the inner quadruple and outer binary, inferring an estimated outer period of ~2 kyr. It was determined that the fainter of the two resolved components is an 8.217 day eclipsing binary, which orbits the inner quadruple that contains two eclipsing binaries with periods of 1.570 days and 1.306 days. MCMC analysis of the stellar parameters has shown that the three binaries of TIC 168789840 are "triplets”, as each binary is quite similar to the others in terms of mass, radius, and Teff. As a consequence of its rare composition, structure, and orientation, this object can provide important new insight into the formation, dynamics, and evolution of multiple star systems. Future observations could reveal if the intermediate and outer orbital planes are all aligned with the planes of the three inner eclipsing binaries.
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