G2 Cloud Likely Contains White Dwarf Star: Luminosity Unchanged


On May 2nd, astronomers A. Ghez, et al. reported on observations of the G2 Cloud which they conducted on March 19th and 20th using the Keck Infrared Telescope; see Astronomer’s Telegram, Report 6110.  They note that they were observing at a time the cloud should have been near its orbital periapse (closest approach to the Galactic core), and found the cloud to be still intact.  From this they concluded that the G2 cloud must contain an embedded star otherwise it could not have survived intact in the presence of the very strong gravitational tidal forces being exerted on the cloud as well as the fierce wind being put out by the galactic core.  In a recent article posted in the Scientific American blog, Seth Fletcher wrote:

“Before the observation, Ghez and her colleagues took bets on the outcome. “If it’s a dust cloud, it won’t be there,” Ghez said, because it will have been torn to pieces. “If it’s a star, it will.”  Both nights, there it was. “We saw G2, clear as day,” Ghez said…  ”The simple gas cloud hypothesis can be ruled out,” she said.

Ghez also suggests that the G2 cloud may contain a binary star system.  So here we see that she concurs with the suggestion that there may actually be two stars hidden within G2.  Ghez was one of the 73 astronomers that I had written to back in January suggesting this idea.  She also noted that most theories have predicted that the G2 cloud should have gotten brighter as it got closer to the Galactic core, but observations have instead shown that hasn’t happened.  Speaking of the G2 cloud she said, “Not only do you see it and it’s compact, but it hasn’t changed brightness at all.”  “We’re trying to come up with a theory that passes Occam’s Razor.”

According to astronomer Stefan Gillessen, the fact that the cloud did not brighten noticeably as it approached the galactic core casts doubt on a theory that a faint star could be hidden within it, because such a star, if present, would heat up as the cloud drew closer to the core and would give off more hot, bright gas through evaporation; see article posted on the Daily Galaxy news website.   Gillessen said, “What we have observed so far is completely consistent with a simple gas cloud,” basing his conclusion on the constancy of the cloud’s constant luminosity.  But, according to the Daily Galaxy theoretical astrophysicist Avi Loeb, who has championed the star theory, “isn’t ready to give up on it yet. He points out that the cloud has so far remained intact and follows an elliptical orbit, as would be expected for a star”.  So, Loeb agrees with Ghez that the cloud should contain a star.

As we see, astronomers are confused by the G2 cloud observational results.  So how do we resolve this paradox, a cloud that stays together as though it were being continuously generated by a star’s stellar wind, and yet not contain a star that would brighten as it approached the core?  In my opinion, the paradox may be resolved if the embedded star is not a main sequence star, but rather is a white dwarf, i.e., a bare stellar core.  There are several reasons why a white dwarf would not be expected to brighten as it approached the Galaxy’s supermassive core.

1) A white dwarf generates a very deep gravity potential well.  Its surface gravity potential would be around 250 times greater than that of the Sun and its average internal gravity potential would be around 1000 times greater than the Sun’s surface gravity potential.  By comparison, when the G2 cloud was at its pericenter distance of about 150 AU from the Galaxy’s core Mother star, its gravity potential would be only around 270 times the Sun’s surface gravity potential.  This would deepen the white dwarf’s self-generated gravity potential well causing it to be about about 25% deeper when the white dwarf was at pericenter.  This would result in a comparable 25% increase in the star’s overall genic energy production which is far less than the more than 20 fold increase in luminosity expected due to the rise in genic energy if the star were instead a one solar mass star, as discussed in last year’s news posting.

2) A second reason why a white dwarf would not brighten as much is that it has a much smaller cross section than a main sequence star.  White dwarfs are typically two percent the diameter of the Sun, hence less than a thousandth of the Sun’s cross sectional area.  Consequently, any cosmic ray heating of its surface by the Galactic core cosmic ray wind would be over a thousand fold less, thereby producing a negligible contribution to any luminosity increase.

3) A third reason why a white dwarf would not brighten as much is because tidal forces exerted on it by the Galactic core would be smaller in proportion to its smaller diameter.  Hence heating due to tidal forces would be over a thousand fold less than those acting on a main sequence star, making such tidal heating effects also negligible.

Hence, for all these reasons, a white dwarf would be expected to maintain an almost constant luminosity as it approached the Galactic core.  Accordingly, any mass loss that the white dwarf was undergoing would also not rise much.  Hence the size and density of the gas cloud the star was generating would show little change as G2 approached pericenter.  Most of the infrared luminosity of the G2 cloud is believed to come from the cloud’s interaction with the Galactic core’s cosmic ray and gas wind, and not from the radiation of  its embedded star.  Hence the cloud would expect to show relatively little change in luminosity.

 Perhaps the reason why astronomers have not considered the possibility of this star being a white dwarf is because standard astrophysical theory assumes that a white dwarf is either a dead remnant or cooling off core that has already expelled its atmosphere.  Yet there are white dwarfs that are seen to be actively expelling a strong stellar wind.  One example is the hot DA type white dwarf known as EGB 6 which has an M type red dwarf companion star (M ~ 0.05 to 0.5 solar masses) orbiting it at a distance of about 95 AU away.  This binary is seen to be surrounded by a compact emission nebula (CEN) estimated to be about 80 AU in diameter, in turn surrounded by a 7 light-year-diameter planetary nebula; see image at the top of this posting.  Observations indicate that in order to explain the outflowing gas in this nebula its central white dwarf and companion must be losing mass at the rate of between 10-9 to 10-5 solar masses per year; see paper by Liebert, et al. (2013).   Liebert et al. hesitatingly attribute this wind to the white dwarf primary since, according to standard astrophysical theory, such a stellar core is supposed to already have ejected its atmosphere over 105 years earlier and hence should show no mass loss activity.  Subquantum kinetics, on the other hand, predicts that hot white dwarfs are active matter creation centers and also heat themselves at a prodigious rate from internally generated genic energy.  Hence mass loss rates in the observed range are entirely expected in these hotter more active white dwarfs.  So it is entirely possible that the G2 cloud could be generated by a central white dwarf.  This mass loss rate for EGB 6 compares to the rate of 4 X 10-8 solar masses per year that Scoville and Burkert have estimated for the mass loss from the star hypothesized to be embedded in the G2 cloud and the diameter of its compact emission nebula is approximately the size of the G2 cloud emission nebula.

The white dwarf hypothesized here to lie within G2 may not be a solitary star.  It could be surrounded by a jovian planet or brown dwarf star.  A brown dwarf is sufficiently small that any increase of its internal luminosity resulting from its pericenter passage of the Galactic core would be masked by the more or less constant emission of the white dwarf primary.  White dwarfs have been seen in binary association with a brown dwarf, as in the case of NLT T 5306 whose brown dwarf secondary is estimated to have a mass of > 0.05 solar masses, or CSS 21055 which is estimated to have a brown dwarf  of between 0.03 and 0.07 solar masses (Steele, et al. 2012).

It is estimated that around 0.5% of the white dwarf population are accompanied by brown dwarfs.  We may roughly assume that an equal percentage of white dwarfs are orbited by planets.  Consequently, if the G2 cloud contains a white dwarf primary star instead of a main sequence star as astronomers previously hypothesized, then there is probability of only about 1% that it will have a binary companion (planet or brown dwarf).  This is far smaller than the percentage of 40% to 80% that we were previously suggesting on the assumption that G2′s embedded star is a main sequence star of mass 1 to 10 solar masses.  Hence the chance of a companion being separated and ultimately crashing onto the galactic core is about 50 fold less than the 3% to 8% chance that we had previously estimated.  Moreover in a subsequent posting, we will discuss a new computer simulation study that indicates that the G2 cloud’s present orbital trajectory is such that, even if the cloud did contain a binary system, it is extremely unlikely that the Galactic core would be able to capture and consume the companion body.  Hence the risk of a superwave occurring within the next year or two is significantly reduced. 

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