Inflation of 430-parsec bipolar radio bubbles in the Galactic Centre by an energetic event

The Galactic Centre contains a supermassive black hole with a mass of four million Suns¹ within an environment that differs markedly from that of the Galactic disk. Although the black hole is essentially quiescent in the broader context of active galactic nuclei, X-ray observations have provided evidence for energetic outbursts from its surroundings². Also, although the levels of star formation in the Galactic Centre have been approximately constant over the past few hundred million years, there is evidence of increased short-duration bursts³, strongly influenced by the interaction of the black hole with the enhanced gas density present within the ring-like central molecular zone⁴ at Galactic longitude |l| < 0.7 degrees and latitude |b| < 0.2 degrees. The inner 200-parsec region is characterized by large amounts of warm molecular gas⁵, a high cosmic-ray ionization rate⁶, unusual gas chemistry, enhanced synchrotron emission^7,8, and a multitude of radio-emitting magnetized filaments⁹, the origin of which has not been established. Here we report radio imaging that reveals a bipolar bubble structure, with an overall span of 1 degree by 3 degrees (140 parsecs × 430 parsecs), extending above and below the Galactic plane and apparently associated with the Galactic Centre. The structure is edge-brightened and bounded, with symmetry implying creation by an energetic event in the Galactic Centre. We estimate the age of the bubbles to be a few million years, with a total energy of 7 × 10⁵² ergs. We postulate that the progenitor event was a major contributor to the increased cosmic-ray density in the Galactic Centre, and is in turn the principal source of the relativistic particles required to power the synchrotron emission of the radio filaments within and in the vicinity of the bubble cavities.

Help-seeking behaviour of hearing-impaired persons aged > or = 55 years; effect of complaints, significant others and hearing aid image

OBJECTIVE

To determine factors influencing help-seeking behaviour in hearing-impaired persons aged > or = 55 years

MATERIAL AND METHODS

The study comprised 1,419 persons (480 females, 939 males) aged > or = 55 years who participated voluntarily in a driving test. Pure-tone audiometry was performed in all subjects. Participants without a hearing aid with an average hearing loss of > or = 30 dB in the better ear for the frequencies 0.5, 1, 2 and 4 kHz were asked how they perceived their hearing by means of a structured questionnaire. The questionnaire provided insight into why some hearing-impaired people seek help from a general practitioner (GP) and others do not. Four factors were examined.

RESULTS

A total of 483/1.419 (34%) participants tested had a hearing loss exceeding 30 dB. Fewer than half of these had visited their GP with complaints of hearing impairment. Of those who had not sought help from a GP, 57% nevertheless judged their hearing as poor. Social pressure exerted by significant others was less in the non-consulters group. Hearing aid image did not differ significantly between the two groups.

CONCLUSION

The help-seeking behaviour of hearing-impaired elderly people is related to the degree of hearing disability and the social pressure exerted by significant others as well as the willingness to try hearing aids.