Update to the Story on the G2 Cloud's
Approach to the Galactic Core
Recent observations of the G2 cloud made in the near infrared at the Keck Observatory indicate that the G2 cloud will reach its closest approach to the Galactic center around mid March of 2014 instead of June of this year. In their paper preprint, astronomers Phifer, et al. place the date of the G2 cloud's closest encounter with the Galactic core at somewhere between the end of January 2014 and the beginning of May 2014 with a median date of mid March. Moreover they estimate that G2's orbit will take the cloud twice as close to the GC than previously thought. The distance of closest approach is now predicted to be 130 astronomical units (AU) rather than 266 AU, as previously thought. See Astrobites Synopsis
The revised trajectory for the G2 cloud dramatically increases the chances that a star hidden within the cloud might have companion stars or planets ripped from it by tidal forces and ultimately consumed by the core. Since tidal force varies as the inverse cube of distance from a massive celestial body, this means that the G2 cloud will be subjected to tidal forces 8.5 times greater than previously estimated. Also since the radiation flux from the Galactic core varies as the inverse square of radial distance, the G2 cloud and its hidden star will be subject to a cosmic ray energy flux and galactic wind energy flux 4 times greater than previously supposed. Another factor disrupting an embedded star or planet is the celestial body's internal genic energy flux which depends on the value of the ambient gravity potential. If the G2 cloud is to approach twice as close to our Galaxy's supermassive core as had been previously thought, this will cause the genic energy output of embedded planets or stars at pericenter to be twice as large as had previously been estimated. (More will be said about these mechanisms below.)
In a Starburst Foundation forum posting made last October, I had presented the possibility that the G2 cloud may harbor a jovian planet or brown dwarf, an idea that had also been suggested by Murray-Clay and Loeb. They proposed that the G2 cloud may contain an unseen low-mass star that is surrounded by a dust and debris accretion disc and that the material in this accretion disc has been evaporated to produce the enveloping G2 cloud as a result of exposure to ionizing radiation or because the accretion disc had been tidally disrupted by previous orbital encounters with the Galactic core. The idea I proposed agrees with their idea of a low mass star or brown dwarf being present. But I believe that the G2 cloud was generated because the contained star or planet has been expelling its atmosphere due to an enormous amount of internal heating it is currently undergoing. Although some of the generated G2 nebula could have come from evaporation of a disc of material orbiting the star, I believe that the main contributor is the atmosphere of the embedded star or planet.
Currently, the idea that the G2 cloud may have an embedded mass has gained more widespread acceptance following the discovery that the cloud is very compact, only about 100 AU in length. In fact this past March, astronomers Scoville and Burkert posted a paper in which they suggest that the G2 cloud may contain a 2 solar mass T Tauri star that is undergoing rapid mass loss, thereby generating the surrounding cloud. T Tauri stars have inflated photospheres typically 2 to 4 times the size of our sun and can be up to an order of magnitude overly luminous. Standard astronomical theory considers a T Tauri star to be an early type star that is accreting gas from its immediate environment to become a main sequence star. But, it is generally recognized that the region within a few light years of the Galactic core is too disruptive to allow star formation and growth through gas accretion. Scoville and Burkert do not address this problem. They do not explain how in such a turbulent environment a star could be surrounded by an accretion disc for long enough to allow it to develop into a T Tauri star. In my opinion, their suggestion is correct that the embedded star could resemble a T Tauri star whose photosphere is very expanded, overly luminous and in the process of discharging a large quantity of gas. However their suggestion that this process is fueled by matter accretion from a protoplanetary accretion disc, I believe, is off the mark. The real cause of the generation of the G2 cloud is the star's entry into the unique Galactic core environment and the consequent stellar heating that occurs there. It has nothing to do with the star accreting a disc of debris that it may have transported with it on its inward journey.
The T Tauri star idea that these astronomers have proposed in many respects resembles what I had suggested in my forum posting last October. I had proposed that the G2 cloud may contain a brown dwarf having a mass of 50 Jupiter masses which has inflated to as much as 3 times the diameter of the Sun and is undergoing a high rate of mass loss as a result of the internal heating. As I explained in my earlier posting, a star approaching the Galactic core would behave as a T Tauri star (would be radially expanded, overluminous, and outgassing its atmosphere to generate the surrounding G2 cloud) because of the enormous amount of genic energy it would be producing internally and because of the large cosmic ray flux it would be intercepting from the GC. In fact, in my opinion, any star approaching close to the GC would be expected to outgas and generate a compact ionized gas cloud similar to the G2 cloud. Of course, the genic energy concept is not widely known in mainstream science in spite of its predictive success. But, knowledge of this mechanism makes all the difference in being able to understand what is currently transpiring within the G2 cloud, and what will continue to transpire as the G2 cloud approaches pericenter in March 2014.
Scoville and Burkert also suggest that the ion wind that is continuously emitted from the Galactic core impacts the G2 cloud and compresses it inward on this upwind side to form a bow shock around the star, the front of this shock reaching inward to as close as 13 AU from the embedded stellar mass. They estimate the entire G2 cloud to have a length of 100 AU and to reside mostly on the downwind side of the star. It should look similar to the cloud shown in this video below.
Animation showing a star with accretion disc embedded inside a knot of dust.
(courtesy of NASA and the James Webb Space Telescope)
Now, with the recent prediction that the G2 cloud should actually approach to within 130 AU of the core, we see that the cloud's diameter is about as large as its closest distance of approach to the core. In the model of Scoville and Burkert, there is a 100% certainty that the cloud will become accreted onto the Galactic core. They find that all gas in the G2 cloud that is lies more than 1 to 3 AU from the star will be tidally stripped away, resulting in an accretion of up to 0.1 earth masses onto the Galactic core.
I predict that the energy output and mass loss rate of the embedded star will rise substantially in the next 10 months as the G2 cloud approaches its orbital pericenter and will result in far greater accretion onto the core than predicted by Skoville and Burkert. The total gas accretion onto the core may perhaps be as great as half an earth mass. However, this alone would produce at most a 50% average rise in the energy output from the core (Sgr A*) over perhaps several months time. As mentioned in my earlier posting, in 2001 the core was observed to produce a much larger magnitude increase in energy flux of about 3 fold over a period of one hour without any serious consequence to the Earth.
[April 16, 2014 update: No rise in X-ray emission from the core has been detected as of now. This implies that the cosmic ray and gas wind from the core is so intense that it prevents any of gas stripped away from the G2 cloud from falling into the core.]
The real danger is if the G2 cloud contains not one star, but two. That is, there is the possibility that the cloud may harbor a close binary star system consisting of a primary star orbited by a lesser massive companion star or of a star orbitted by one or more jovian planets. Current observations cannot exclude this possibility since dust obscuration prevents us from peering very deep into the G2 cloud. This binary star/planetary system scenario would look something like that seen in the video below. The dust and gas being dispersed to form the G2 cloud would be coming not only from a possible planetary disc around the star, but also from the central star itself and from any planets that may be orbiting it since planets would be actively expelling their atmospheres as well.
Animation showing a photo-evaporating debris-laden planetary disc that surrounds a star and generates its circumstellar nebula. (courtesy of ESA and M. Kornmesser)
It is known that a very high percentage of stars in our Galaxy are either binary star systems or are single stars orbited by jovian planets. Hence there is a high probability that the G2 cloud may harbor such a multi-body system. If this is the case, there is the danger that the Galactic core may tidally strip away and consume the system's lower-mass companion star or one or more of the star's planets at the time of pericenter passage of the core. For example, a one solar mass star similar to the Sun would have a tidal radius of 0.5 to 1 AU at its orbital pericenter which means that any stellar companions, planets, or debris orbiting at radii greater than this could be tidally stripped away from their orbit about the primary star and ultimately be pulled into the galactic core.
In the case where an entire 100 jupiter mass brown dwarf were to plunge into the Galactic core in one discrete event, the energy release would be equivalent to that released in a hypernova, the most powerful of known supernova exposions (~1053 ergs). This could be enough to jump-start the Galactic core into a Seyfert state and generate a potentially lethal superwave. If this amount of energy were delivered within the space of one day, this would release energy at the rate of 1048 erg per second, giving a luminosity one hundred thousand times greater than the cosmic ray luminosity estimated to currently be coming from Sgr A* (based on my estimate of 1043 ergs/s -- see Subquantum Kinetics), and equivalent to the luminosity radiated by the active core in a Seyfert galaxy.
We will know if such a scenario is going to occur by closely monitoring the G2 cloud. As the cloud nears pericenter, if we see it appear to divide and spawn off a subcloud that begins rapidly accelerating directly toward the Galactic core, we will know this worst case scenario is about to occur. This subcloud will contain within it the binary companion star or jovian planet that has been tidally stripped off from the parent star. At this point we will have about four to five months
two months before its possible impact on the core, at which point an exceedingly bright gamma ray burst and cosmic ray spike will be detected on Earth, far greater than any we have seen until now. The superwave will have arrived at our doorstep, possibly heralded by earthquakes occurring a few days before.
[April 16, 2014 update: The estimate previously given here of there being a two month delay from the date of cloud splitting until possible core impact was in error. The best current estimate without doing actual simulations is 4.5 months.]
Stellar Heating Effects in the Vicinity of the Galactic Core
A one solar mass star that approaches to within 130 AU of the Milky Way's supermassive galactic core will be subject to a gravity potential field that is 1485 times the surface gravity potential that such a star would generate due to its own mass, and about 186 times the average value of the gravity potential in its interior. In a one solar mass star that is distant from the Galactic center, I have estimated that about 12% of its total energy output is in the form of genic energy, the remaining 88% arising from nuclear fusion. When that same star is brought to within 130 AU of the Galactic core, its genic energy output will rise 186 fold causing it to exceed its former luminosity by 23 fold! Due to this rise in luminosity, the star's diameter would expand until it reached perhaps 4 times its former size.
Figure 1 shows how the luminosity of a one solar mass star embedded within the G2 cloud would increase as it progressively approached its orbital pericenter. The red curve is the star's excess luminosity due to its increase in genic energy output and the blue curve is the star's total excess luminosity where we add in also energy the star receives due to heating of its interior by incident Galactic core cosmic rays.
If the embedded star were a 100 Jupiter mass red dwarf, its luminosity which normally would be about 0.09% of the sun's luminosity would soar 2,500 times to 2.3 solar luminosities. So in this close vicinity to the Galactic core, stars would be rapidly losing their atmospheres, even if they were below their Eddington Limit. In a forum posting made last October, I had warned of this stellar mass loss effect which could generate large quantities of gas which could ultimately fall into the Galactic core. The new orbital trajectory for the G2 cloud substantially enhances this danger.