# 3C273 jet mass estimate

In this picture of 3C273, we can see a jet-estimated to be around 200,000 light-years long-being emitted.

I'm trying to find an estimate for the mass of the jet. It's a stream of electrons, accelerated through synchrotron radiation (see here). There seems to be lots of information on its spectroscopic properties and the mass of the quasar (886 million solar masses), but I can't find an estimate for the mass of the jet itself. Does anyone know of a source I could look at to give me some idea?

Trigger Warning: Major hacking going on here. [edited from 1 ly to 1000 ly diameter] Scaling from the image, I'll approximate the jet diameter as 1000 ly . So there's a volume of roughly 2e4*1e6 * pi/4 cubic ly. For absolutely no good reason, I'll propose an electron ejection density of 1E6 per cubic km -- at least those are round numbers and easily scalable if anyone can find references to actual calculations/measurements --, so using 1 cubic ly = 8.468e+38 cubic km, I get 1.33e+56 electrons in the jet.

## The extremely hot heart of quasar 3C273

Chandra X-Ray Observatory image of quasar 3C273. Its extremely powerful jet probably originates from gas that is falling toward a supermassive black hole. Image via Chandra.

By combining signals recorded from radio antennas on Earth and in space – effectively creating a telescope of almost 8-Earth-diameters in size – scientists have, for the first time, gotten a look at fine structure in the radio-emitting regions of quasar 3C273, which was the first quasar known and is still one of the brightest quasars known. The result has been startling, violating a theoretical upper temperature limit. Yuri Kovalev of the Lebedev Physical Institute in Moscow, Russia, commented:

We measure the effective temperature of the quasar core to be hotter than 10 trillion degrees!

This result is very challenging to explain with our current understanding of how relativistic jets of quasars radiate.

These results were published on March 16, 2016 in the the Astrophysical Journal.

A March 29 statement from the Max Planck Institute explained:

Supermassive black holes, containing millions to billions times the mass of our sun, reside at the centers of all massive galaxies. These black holes can drive powerful jets that emit prodigiously, often outshining all the stars in their host galaxies. But there is a limit to how bright these jets can be – when electrons get hotter than about 100 billion degrees, they interact with their own emission to produce X-rays and Gamma-rays and quickly cool down.

But, once again, quasar 3C273 has surprised us, this time with a temperature much higher than that thought possible.

To obtain these new results, the international team used the space mission RadioAstron – an Earth-orbiting satellite, launched in 2011 – which employs a 10-meter radio telescope aboard a Russian satellite. RadioAstron is what astronomers call an Earth-to-space interferometer. In other words, multiple radio telescopes on Earth are linked to RadioAstron to obtain results not possible from any single instrument. In this case, the Earth-based telescopes included the 100-meter Effelsberg Telescope, the 110-meter Green Bank Telescope, the 300-meter Arecibo Observatory, and the Very Large Array. These astronomers’ statement said:

Operating together, these observatories provide the highest direct resolution ever achieved in astronomy, thousands of times finer than the Hubble Space Telescope.

The incredibly high temperatures weren’t the only surprise from this study of quasar 3C 273. The RadioAstron team also discovered an effect they said has never seen before in an extragalactic source: the image of 3C 273 has a substructure caused by the effects of peering through the dilute interstellar material of the Milky Way. Michael Johnson of the Harvard-Smithsonian Center for Astrophysics (CfA), who led the scattering study, explained:

Just as the flame of a candle distorts an image viewed through the hot turbulent air above it, the turbulent plasma of our own galaxy distorts images of distant astrophysical sources, such as quasars.

These objects are so compact that we had never been able to see this distortion before. The amazing angular resolution of RadioAstron gives us a new tool to understand the extreme physics near the central supermassive black holes of distant galaxies and the diffuse plasma pervading our own galaxy.

Bottom line: Scientists combined radio telescopes on Earth and with the Earth-orbiting radio telescope RadioAstro to learn that the famous quasar 3C273 has a core temperature hotter than 10 trillion degrees! That’s much hotter than formerly thought possible.

## 3C273 jet mass estimate - Astronomy

Quasars look like any normal star through an optical telescope. It wasn&rsquot until the 1950&rsquos, when radio astronomy was first developed, that astronomers realized these extragalactic objects are emitting massive amounts of radio energy. This important discovery was named a quasar, short for &ldquoQuasi-stellar radio source&rdquo. By waiting for known radio sources to pass behind the moon, optical and radio data could be combined to give astronomers the precise location of quasars in the sky.

Quasars are among the most distant, energetic objects ever observed. Even though individual quasars are brighter than hundreds of galaxies put together, many are smaller than the size of our own solar system.

Radio astronomers use a system of numbers to name objects in the sky. 3C273 was named in the 3rd Cambridge catalog as the 273rd radio source identified. 3C273, along with 3C48, were the first quasars to be identified. These objects had bizarre spectra unlike any ever studied before. In 1963 astronomers Maarten Schmidt (3C273) and Jesse Greenstein and Thomas Matthews (3C48) noticed that the spectrum made sense if it was simply an extremely large redshift. In other words, 3C273 was moving away from us at an incredible one-tenth the speed of light.

Recent discoveries have lead to new insight into how quasars might work. Learning more about 3c273 and other quasars helps to discover more about the history, large-scale structure, and future of our universe. Our own group of galaxies is about ten billion years old. In some cases, the photons we observe from the most distant quasars are comparable to the age of our galaxy!

Thanks to radio and X-ray observation, it is now apparent that the centers of galaxies like our own are home to as-of-yet unexplained energetic reactions. Some galaxies are called active galaxies, as they are further away and their nuclei emit far more radiation than galaxies like our own. Quasars are the most energetic and distant of all three objects. It is believed that the nucleus of a quasar is so bright that it hides the relatively dim surrounding galaxy. The activity in the nuclei of galaxies and active galaxies has similar characteristics to the activity taking place in quasars, and since it is easier to observe, it helps verify theories that explain how quasars work.

What is the engine behind the massive amounts of energy released by quasars? A clue is provided by the jet of 3C273, a radio, optical and X-ray spike that extends over a hundred thousand light years into space. This pattern points to a rotating, supermassive object. According to theory, matter from the surrounding galaxy orbits this object in what is called an accretion disk. Whenever matter from the disk is pulled by gravity into the center, the resulting electromagnetic forces could produce a beam of high-energy particles that would be observed as a jet at radio, optical and X-ray energies.

LEFT:Optical of 3C273 (Credit:NASA/STScI)
RIGHT: X-ray of 3C273 (Credit: NASA/CXC/ SAO/H. Marshall et al.)

Any object with enough mass to produce these jets of energy would certainly collapse on itself due to its own gravity. Also, both quasars and active galaxies are seen to have massive, dark objects at their core. In fact, the only object known to theory that fits these criteria is a black hole, an object so massive that not even light can escape its gravitational pull!

## Variability of blazar 3C 273 examined by astronomers

Spectra of 3C 273 at different activity states. The red spectrum corresponds to the date of the highest continuum flux observed, the blue spectrum corresponds to the lowest continuum flux observed, and the green spectrum corresponds to a medium point in continuum flux between the red and blue spectra. Credit: Fernandes et al., 2020.

Using data from space observatories and ground-based telescopes, astronomers have investigated variability of a blazar known as 3C 273. The new study, presented in a paper published July 6 on the arXiv pre-print server, sheds more light on the emission from this source.

Blazars are very compact quasars associated with supermassive black holes at the centers of active, giant elliptical galaxies. Based on their optical emission properties, astronomers divide blazars into two classes: flat-spectrum radio quasars (FSRQs) that feature prominent and broad optical emission lines, and BL Lacertae objects (BL Lacs), which do not.

Located some 2.44 billion light years away, 3C 273 is one of the closest quasars to Earth, and is optically the brightest such object in the sky. Given that 3C 273 was the first discovered quasar, it has been comprehensively studied in different wavelengths. The observations show that it is a blazars of the FSRQ subclass, highly variable from radio to gamma-rays.

A team of astronomers led by Sunil Fernandes of the University of Texas at San Antonio took a closer look at the variable nature of 3C 273. They analyzed observational data of this blazar obtained between 2008 and 2015 with various instruments, including NASA's Fermi spacecraft and Steward Observatory.

"We present multiwavelength light curves and polarimetric data of the Flat Spectrum Radio Quasar 3C 273 over eight years. The wavelength range of our data set extends from radio to gamma-rays," the astronomers wrote in the paper.

In general, the millimeter and radio emission in blazars are dominated by synchrotron emission from the blazar's jet. However, in the case of 3C 273, the dominant component of the optical emission does not share the synchrotron origin that the 1 mm and the 15 GHz emission have. This suggests that the optical emission is dominated by thermal emission from the accretion disk during the studied period.

According to the paper, no correlation was found between the gamma-ray luminosity and the gamma-ray spectral index. This finding may indicate that the energetics of the gamma-ray production processes causing the variability in 3C 273 are different from other blazars. However, the astronomers noted that the lack of this correlation might be also due to sampling problems, therefore further studies of the blazar are required in order to confirm this.

The study has also identified an anti-correlation between the 15 GHz and V-band light curves. The researchers assume that it could be due the fact that an ejection from the blazar's jet, and therefore an increment in radio synchrotron emission, is caused after the inner part of the accretion disk falls into the black hole. This causes a drop in the accretion disk emission.

"A scenario that fits the observed behavior, is the case where the inner part of the accretion disk falls into the black hole, which causes a drop in the X-ray emission this event is normally followed by the ejection of a component from the jet base," the authors of the paper concluded.

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## Monster Quasar Discovered

Astronomers in Australia say they have found the hungriest heart in all the cosmos. It is a black hole 20 billion times the mass of the Sun eating the equivalent of a star every two days. The black hole, named SMSS J215728.21-360215.1, is 12.5 billion light years away from earth (redshift of 4.75). It expands 1 per cent every million years and it devours a mass equivalent to our Sun every two days. It is the most powerful quasar found to date. (The quasar pictured to the left is a NASA artist's illustration.)

"The black hole is growing so rapidly," said Christian Wolf of the Australian National University (ANU) who led the team that found it, &ldquothat it is about 10,000 times brighter than the galaxy it lives in. So bright, that it is dazzling our view and we can&rsquot see the galaxy itself."

The blaze from material swirling around this newly observed quasar is as luminous as about 700 trillion Suns, according to Dr. Wolf and his collaborators. If it were at the center of our own galaxy, the Milky Way, it would be 10 times brighter than the moon and bathe the earth in so many X-rays that life would be impossible. Per Wikipedia, SMSS J215728.21-360215.1 is the most "luninous quasar" ever discovered - 6.95 × 10^14 Suns.

The massive quasar appears as a reddish pinprick of light in the southern constellation Piscis Austrinus. It was one of many possible quasars that are part of the SkyMapper Southern Sky Survey (SMSS) by Dr. Wolf and his colleagues who are building a comprehensive digital survey of the entire Southern Sky. Dr. Wolf and his team confirmed their findings by cross-matching them with data released by the GAIA spacecraft, which is triangulating the distances to stars, looking for objects that do not appear to move and are thus very, very far away.

Astronomers have uncovered quasars dating as far back as about 700 million years after the Big Bang (ULAS J1342+0928 - redshift 7.54). Despite their high luminosity these distant quasars are are very difficult to find and are extremely faint to our scientific eyes because of their great distance in a dusty universe. Only 40 known quasars have a redshift higher than 6.0, the yardstick that defines the boundary of the early universe.

Astronomers are at a loss to explain how such an enormous black hole could have formed so early in cosmic history - so very soon after the first stars and galaxies emerged. A quasar is an extremely bright cloud of mostly gas in the process of being pulled into a huge black hole. As the material accelerates towards the black hole, it heats up emitting an extraordinary amount of x-ray and gamma energy which then pushes away other material falling behind it. This process, known as radiation pressure, is thought to limit the "growth rate" of black holes.

However, this black hole gained enormous mass in a very short period of time which differs from the current theory of black hole growth. How it got so big so quickly after the Big Bang adds to a mystery about the origin of supermassive black holes that occupy the centers of galaxies, often weighing in at more than a billion Suns. Discoveries such as J215728.21-360215.1 might push astronomers in favor of the &ldquodirect-collapse&rdquo formation scenario, in which pristine gases collapse on their own to form black holes directly. Thus this ultra-luminous huge quasar provides a unique laboratory to study black hole formation in the early universe. Top

## 3C273 jet mass estimate - Astronomy

The paradigm of QSO physics is that the energy is freed by accretion of matter in a massive black hole. This paradigm allows some simple estimates:

The Eddington luminosity for which gravitational attraction compensates radiation pressure is:

Using the bolometric luminosity of 3C 273 deduced in Sect. 3.5 we thus estimate that provided that the bulk of the luminosity is emitted isotropically the mass of the central black hole is

10 9 solar masses. The corresponding gravitational radius is

3 . 10 14 cm. The mass accretion rate can be estimated from the luminosity L by:

where is the efficiency of the conversion of rest mass to radiation.

Using the same luminosity as above and an efficiency

10% typical of accretion onto black holes we deduce a mass accretion rate

1.3 . 10 27 g s -1 or about 10 solar masses per year. Not surprisingly, these numbers are close to those deduced from accretion disc models.

Going beyond these estimates requires understanding of how the energy liberated by the accretion process is transformed in the radiation we observe across the electromagnetic spectrum. This understanding is still widely lacking, we can, however, list some of the elements that do play a role.

Highly relativistic electrons and magnetic fields must belong to any model of 3C 273 (and other radio loud AGN) as shown by the presence of synchrotron radiation. Their energy densities are very inhomogenous and partly organized in small packets some of which at least are accelerated to relativistic bulk velocities along complex paths to form the observed small scale jet. It is probable that the electrons are accelerated to highly relativistic energies in shocks and that they thus aquire the energy that they radiate from the kinetic energy of some underlying flows.

Another indication of fast flows is the presence of the broad lines which indicate that the material surrounding the black hole has velocities of the order of 10 4 km/s. It has not been possible to find in the line variability pattern the signature for a dominantly ordered velocity field (expansion, accretion or rotation). One, therefore, concludes that a large fraction of the velocity field is of a turbulent nature. In these circumstances, the presence of shocks where streams of matter collide is difficult to avoid. It is interesting to note that thermalising Hydrogen gas with bulk velocities of the order of 10 4 km/s will produce a gas of T

5 . 10 9 K. A temperature close to the one needed to Comptonise the UV photons to X-rays with a slope as observed (Walter & Courvoisier 1992).

A fraction of the UV and higher energy radiation is reprocessed by gas to form the broad lines and by dust to give the thermal infrared radiation. The organisation of the broad line emitting clouds is unclear, no cloud confining medium having been found. Whether the optical-UV emission forming the blue bump is itself due to reprocessed X-ray emission is also unclear, mostly because of the absence of the signature of Compton reflection in the X-rays.

There are many different timescales at play. Among those we know there is the few days delay between the UV and optical light curves which imply that the signals ruling the blue bump emission travel at the speed of light. There is also the presence of much longer timescales (of several years) in the visible light curves and correlations which delays of the order of a year or so, between emission components. These timescales are long compared with light crossing times or dynamical times in the vicinity of the black hole. They are, however, short compared to viscous timescales of standard accretion discs. (Courvoisier & Clavel 1991). The presence of these timescales may either indicate that the size of the continuum emitting accretion is of the order of a parsec (similar to the size of the broad line region) or that there exist characteristic velocities of the order of few percent of the speed of light in a region of several gravitational radii. One may also note that the amplitude of the variations at short timescales ( one day

10 gravitational radii over c) is small (few percent (Paltani et al. 1998)). This may indicate that the variations on this timescale are not associated with the regions closest to the black hole, but rather to small regions in an extended object.

There have been many attempts to understand the geometry of the emission regions considering one or several emission components. Most have been based on the presence of accretion discs. Many of the arguments are revised in (Blandford 1990). The addition of a corona being discussed by (Haardt et al. 1994).

(Camenzind & Courvoisier 1983) attempted to understand the continuum emission of 3C 273 in terms of a mildly relativistic wind originating in the core of the object and shocked at some distance. Most of the observed emission in this model was the by product of the shocked material. This model predicted that the variation time scales of the different components was such that the UV varied faster than the X-rays which in turn varied faster than the optical emission. The infrared and gamma ray variability timescales were expected to be the longest. These predictions were soon disproved by observations which led to a revision of the geometry (Courvoisier & Camezind 1989). In this revised geometry the wind is channeled in such a way that the shocked material covers only few percents of the UV source. The shocked material is heated to temperatures such that the UV photons crossing it are Comptonised to X-ray energies. The lag between X-ray and UV fluxes may be understood naturally in this geometry (Paltani et al. 1998).

(Courvoisier et al. 1996) have considered whether accretion of matter could be in the form of stars rather than gas. In their model the gravitational energy is radiated following collisions between stars in the vicinity of a black hole. First order considerations showed this to be a possible alternative to understand the variability of AGN and its dependence on luminosity. This also points to the little studied question of the interaction between the active nucleus and the surrounding stellar population.

It is thus clear that although the main elements of the AGN model have been in place for more than 30 years, often following pioneering observations of 3C 273, much remains to be understood. AGN are considerably more complex than many of us anticipated. This complexity together with the extreme properties they show make them fascinating object to study.

### Acknowledgments

This work is based on a long term effort by a large set of colleagues who have participated in the gathering of data and in many discussions over the years. I owe a particular debt to M. Camenzind and M.-H. Ulrich for sharing their knowledge with me when this effort began. I would never have been able to write this review without the benefit from many interactions over the years and around the world. Several of my colleagues at the ISDC have given me some very direct help in preparing this review and in particular the figures. They are S. Paltani, M. Polletta and M. Türler. I thank them and also T. Krichbaum, R. Walter and L. Woltjer for reading and commenting the manuscript. A. Aubord and M. Logossou have been of much help in the typesetting. *****

## Astronomers estimate Titan's largest sea is 1,000-feet deep

An artistic rendering of Kraken Mare, the large liquid methane sea on Saturn’s moon Titan. Credit: NASA/John Glenn Research Center

Far below the gaseous atmospheric shroud on Saturn's largest moon, Titan, lies Kraken Mare, a sea of liquid methane. Cornell University astronomers have estimated that sea to be at least 1,000-feet deep near its center—enough room for a potential robotic submarine to explore.

After sifting through data from one of the final Titan flybys of the Cassini mission, the researchers detailed their findings in "The Bathymetry of Moray Sinus at Titan's Kraken Mare," which published in the Journal of Geophysical Research.

"The depth and composition of each of Titan's seas had already been measured, except for Titan's largest sea, Kraken Mare—which not only has a great name, but also contains about 80% of the moon's surface liquids," said lead author Valerio Poggiali, research associate at the Cornell Center for Astrophysics and Planetary Science (CCAPS).

A billion miles from Earth, frigid Titan is cloaked in a golden haze of gaseous nitrogen. But peeking through the clouds, the moonscape has an Earthlike appearance, with liquid methane rivers, lakes and seas, according to NASA.

The data for this discovery was gathered on Cassini's T104 flyby of Titan on Aug. 21, 2014. The spacecraft's radar surveyed Ligeia Mare—a smaller sea in the moon's northern polar region—to look for the mysteriously disappearing and reappearing "Magic Island."

While Cassini cruised at 13,000 mph nearly 600 miles above Titan's surface, the spacecraft used its radar altimeter to measure the liquid depth at Kraken Mare and Moray Sinus, an estuary located at the sea's northern end. The Cornell scientists, along with engineers from NASA's Jet Propulsion Laboratory, had figured out how to discern lake and sea bathymetry (depth) by noting the radar's return time differences on the liquid surface and sea bottom, as well as the sea's composition by acknowledging the amount of radar energy absorbed during transit through the liquid.

It turns out that Moray Sinus is about 280 feet deep, shallower than the depths of central Kraken Mare, which was too deep for the radar to measure. Surprisingly the liquid's composition, primarily a mixture of ethane and methane, was methane-dominated and similar to the composition of nearby Ligeia Mare, Titan's second-largest sea.

Earlier scientists had speculated that Kraken may be more ethane rich, both because of its size and extension to the moon's lower latitudes. The observation that the liquid composition is not markedly different from the other northern seas is an important finding that will help in assessing models of Titan's Earth-like hydrologic system.

Beyond deep, Kraken Mare also is immense—nearly the size of all five Great Lakes combined.

Titan represents a model environment of a possible atmosphere of early Earth, Poggiali said.

One puzzle is the origin of the liquid methane. Titan's solar light—about 100 times less intense than on Earth—constantly converts methane in the atmosphere into ethane over roughly 10 million-year periods, this process would completely deplete Titan's surface stores, according to Poggiali.

In the distant future, a submarine—likely without a mechanical engine—will visit and cruise Kraken Mare, Poggiali said.

"Thanks to our measurements," he said, "scientists can now infer the density of the liquid with higher precision, and consequently better calibrate the sonar aboard the vessel and understand the sea's directional flows."

## A swing in the jet direction at the quasar 3C 273

Sketch of a sheath wrapped around the wide jet in 3C 273. Subject to the single-epoch relativistic jet orientation . [more]

Sketch of a sheath wrapped around the wide jet in 3C 273. Subject to the single-epoch relativistic jet orientation, synchrotron emission of the jet passes through different parts of the sheath. Faraday rotation measures values change from positive to negative in 2003. If the jet turns southwards, only negative rotation measures.

Sketch of a sheath wrapped around the wide jet in 3C 273. Subject to the single-epoch relativistic jet orientation, synchrotron emission of the jet passes through different parts of the sheath. Faraday rotation measures values change from positive to negative in 2003. If the jet turns southwards, only negative rotation measures.

The high-redshift radio source with number 273 in the third Cambridge catalog (also known as 4C +02.32, ON 044, or CTA 053) is one of the best studied objects in very-long-baseline interferometry. New results presented in a publication led by the Bonn astronomer Misha Lisakov reveals changes in the polarisation of the jet which suggest a change in the jet direction during the period 2009-2010 from multi-wavelength studies using the Very Long Baseline Array. The work, presented in the latest issue of The Astrophysical Journal, shows that the jet Faraday rotation measure has changed significantly toward negative values compared with that previously observed. These changes could be explained by a swing of the parsec-scale jet direction, which causes synchrotron emission to pass through different portions of the Faraday screen. The work develops a model for the jet-sheath system in 3C 273 where the sheath is wider than the single-epoch narrow relativistic jet. The wide jet–sheath boundary is about 750 light years downstream from its beginning. Most of the Faraday rotation occurs within the innermost layers of the sheath. Further details on the jet parameters and the impact of this work in the study of other sources can be obtained in the original publication, see here.