Some Conceptual Some Conceptual Problems in CosmologyProblems in Cosmology

Prof. J. V. NarlikarProf. J. V. Narlikar

IUCAA, PuneIUCAA, Pune

3. 3. Anomalous RedshiftsAnomalous Redshifts

in Astronomyin Astronomy

Spectral Shifts

Spectral shifts are very common to astronomical observations.

Spectral Shift

z = (λ - λo)/ λo

Observed wavelength of a line in the spectrum = λThe wavelength expected for the same line in a laboratory

source = λo

Example: Suppose a line is emitted by a laboratory

source at 500 nanometres but is found in an astronomical source at 550 nm. Then its spectral shift = 50/500 = 0.1

Red and Blue shifts: If the observed wavelength has increased above the expected one, we have redshift, and if the observed, wavelength is less than the expected one, we have blueshift.

The Doppler interpretation

The Doppler effect relates the spectral shift to relative motion between the source and the observer:

The Observer finds a spectral shift given by :

1 + z = {1+(v/c) cos } / {1-v2/c2}1/2

a) A source moving radially away is redshifted while a source radially approaching is blueshifted...

b) For a fast moving source the full relativistic formula is to be applied. Thus a source with redshift 2 is radially moving away at speed 4c/5.

c) For small redshifts (z << 1), the Newtonian approximation is ok. For' example, a source with redshift 0.01 is moving away from us at speed 0.01c.

Typical stellar motions in the galaxy produce spectral shifts of both kinds of the order < 10-3

The Doppler shift

The Gravitational Redshift

Einstein's general relativity provides another interpretation of spectral shifts... in terms of motion of a photon across regions of differing gravitational strengths.

From strong field weak field: Redshift

From weak field strong field: Blueshift

Gravitational redshifts from white dwarfs stars are generally < 10-3

The Gravitational Redshift

Cosmological Redshift

Discovered during ~ 1914 by Slipher... Systematic study by Hubble and Humason during the

1920s...

Hubble's law in 1929 in the form of a velocity (V ) - distance (D) relation for extragalactic nebulae...

V = H x D

These redshifts were much greater than the galactic ones known earlier.

Also the blueshifts were very rare...

These can be understood in terms of an expanding universe. If S(t) is the scale factor for expansion, the redshift formula is

1 + z = S(to) / S(t1)

where to and t1 are the time of reception and emission of the light ray.

Example: For a galaxy of redshift 2, the light left when the universe was one third in linear size compared to the present.

The question to be answered is: Is Hubble's law universally true, or are their anomalies where it is violated? If so, how do we understand the anomalies?

Can the Doppler and gravitational options help understand these anomalies? Or do we need something entirely new?

Anomalous redshifts

Arp, Tifft, the Burbidges have argued in favour of the reality of anomalous redshifts...

Generic case: Q : Quasar G : Galaxy both seen very close

to each other so that the probability of their being so close by chance projection effects is negligible, say ≤ ~10-3. Then if they are near neighbours, by Hubble's law their redshifts zG, zQ must be equal.

But if we find zQ >> zG, then it means that at least Q has an intrinsic component of redshift zI such that (1 + zQ) = (1 + zG ) (1 + zI )

Anomalous redshifts

The main galaxy, NGC 7603 is an active, X-Ray bright Seyfert with a redshift of 8,000 km/sec. The companion is smaller with a redshift of 16,000 km/sec and a bright rim where the filament from the Seyfert enters it. The recent measures indicate the filament is drawn out of the low redshift parent and contains the two emission line, high redshift, quasar like objects.

Do such cases Really exist?

If they are real, how do we explain them?

Anomalous redshifts

Explanation of anomalous redshifts

Variable mass hypothesis (VMH): A particle acquires mass through Machian

interaction traveling with the speed of light... If in flat spacetime, all particles were created

at rest at t = 0, then a particle of age t1 will be in touch with all particles lying within the sphere of radius r = c x t1. If the typical inertial interaction from a distance r is 1/r, then the above sphere contributes an inertia t1

2.

If an observer at the present epoch to, in this flat spacetime receives light from another galaxy G at a distance r, then he is comparing the masses of identical type of particles, at epochs to and to-r.

Using the result that all atomic wavelengths scale with the electron mass me as (1/me), the observer will measure a redshift zG given by

1 + zG = (to/ to-r)2

Thus the VMH provides an explanation for ordinary redshift in flat spacetime.

Now if the galaxy G creates a quasar Q at epoch tQ, and ejects it in an MCE, the quasar will have a typical particle mass lower than that in the galaxy. Thus the redshift of the quasar will be

1 + zQ = { to / (to- tQ- r) }2

Thus we will have zQ > zG .

Notice that this produces anomalous redshifts only: there are no anomalous blueshifts, in view of the above inequality.

Dynamics of ejection

In 1980, Narlikar and Das worked out the detailed dynamical equations of motion of ejected matter from a galaxy and applied to Q-G associations.

In recent times X-ray quasars have also been found by Arp concentrated and aligned in the neighbourhood of NGC galaxies. The Das-Narlikar calculations have been applied to them also...

Redshift periodicities

Tifft: cz 36 or 72 km/s in galaxy groups

Redshift periodicities

Tifft: cz 36 or 72 km/s in galaxy groups Burbidge: z = 0.06

Redshift periodicities

Tifft: cz 36 or 72 km/s in galaxy groups Burbidge: z = 0.06 Karlsson:

log (1+z) = 0.089

Redshift periodicities

Tifft: cz 36 or 72 km/s in galaxy groups Burbidge: z = 0.06 Karlsson: log (1+z) = 0.089 Series {zn} 0.06, 0.30, 0.60, 0.96,

1.41, 1.96, 2.64,...

Are they real?

If so... How do we understand them?