Can A Wormhole Be A Black Hole? (Cosmology)

Just search on google, “what are the types of wormholes?”, multiple results will appear on your screen like Morris Throne, Ellis wormhole, Schwarzschild wormhole etc. But, all these, are not at all same. Some are constructed in an artificial manner while, some are exact solutions of general relativity. Belonging to latter class is the wormhole called “Ellis-Bronnikov wormhole (EBWH)”. These wormholes are built by energy-violating Einstein minimally coupled scalar field. Now, Rosaliya Yusupova and colleagues carried out study of accretion onto Ellis-Bronnikov wormhole.

There is an important caveat relating to the stability of EBWH. EBWHs are unstable to perturbations. This means that they should not be existing in the universe today—they should have died almost as soon as they were born. In that case, what is the use of studying accretion to such an object? However, some time ago, the question of (in)stability was analyzed from a completely different standpoint based not on challenging the mechanism of instability but on exploiting the fact that, in general relativity, observations are dependent on the location of the observer. It was then shown that while some observers observe instability of EBWH, there is a nonzero probability that some other observers could observe its stability from different locations. Thus, their accretion scenario is relevant only to the latter types of observers.

They first identified a novel feature of EBWH, namely that it reduces to the Schwarzschild black hole under the combination of a complex wick rotation and an inversion.

Then, they analyzed the profiles of fluid radial velocity, density and the rate of mass variation of the EBWH due to accretion and compared the profiles with those of the Schwarzschild black hole (SBH). Their results are described below:

  • The EBWH velocity profiles remain lower than that of SBH at all radii, showing that the phantom matter also accretes to EBWH. The same behavior also emerges for massless EBWH. As one moves away from the central object, all profiles tend to merge close to one another.
  • The density of fluid accreting to EBWH is less than that accreting to SBH. In the case of massive EBWH, density increases in the vicinity of the throat (and horizon is case of SBH). While the density becomes minimums , near the throat of massless EBWH.
  • The accretion of phantom energy decreases the mass of SBH, but increases the mass of EBWH.
  • Accretion to massless EBWH shares the same patterns as those of the massive EBWH; hence, there is no way to distinguish massive and massless objects by means of accretion flow.
  • For quintessence, dust and stiff matter, it has been shown that the massless EBWH has the highest velocity of accreting fluid, and the SBH profile shows lowest velocity profiles. While, highest density and high values of accreting matter achieved near the central source.
  • Non-phantom accretion (quintessence, dust, stiff matter) increases the mass of SBH but decreases the mass of EBWH.

“The above contrasting behavior of accretion could be the physical signatures of the distinct topologies of the accreting central objects”

— concluded authors of the study

Figure 1. Velocity profile (a), energy density (b) of phantom energy (ω = –2) and rate of change of mass (c) of EBWH versus r/M for different values of γ and m, which satisfies M = mγ = 3/2. For illustration, they used the set of constants A0 = 1, A2 = –1 and A4 = 4 © Yusupova et al.
Figure 2. Velocity profile (a), energy density (b) of quintessence matter (ω = –0.5) and rate of change of mass (c) of EBWH versus r/M for different values of γ and m, which satisfies M = mγ = 3/2. For illustration, they used set of constants A0 = =1/2, A2 = –1 and A4 = 4 © Yusupova et al.
Figure 3. Velocity profile (a), energy density (b) of dust (ω = 0) and rate of change of mass (c) of EBWH versus r/M for different values of γ and m, which satisfies M = mγ = 3/2. For illustration they used the set of constants A0 = –1, A2 = –1, and A4 = 4. © Yusupova et al.
Figure 4. Velocity profile (a), energy density (b) of stiff matter (ω = 1), and rate of change of mass (c) of EBWH versus r/M for different values of γ and m, which satisfies M = mγ = 3/2. For illustration, they used set of constants A0 = –2, A2 = –1 and A4 = 4. © Yusupova et al.

Reference: Yusupova, R.M.; Karimov, R.K.; Izmailov, R.N.; Nandi, K.K. “Accretion Flow onto Ellis–Bronnikov”, Wormhole. Universe 2021, 7, 177. https://doi.org/10.3390/universe7060177


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